Roger Bacon, a 13th century Franciscan philosopher-theologian, began his Opus Majus, “Major Work,” with a discussion on the four obstacles he believed which diverted people from the truth: “Now there are four chief obstacles in grasping truth, which hinder every man, however learned, and scarcely allow any one to win a clear title of learning, namely, submission to faulty and unworthy authority, influence of custom, popular prejudice, and concealment of our own ignorance accompanied by an ostentatious display of our knowledge.” Of the four, Bacon thought the fourth was the worst, and most dangerous: “Should, however, these three errors be refuted by the convincing force of reason, the fourth is always ready and on ever one’s lips for the excuse of his own ignorance, and although he has no knowledge worthy of the name, he may yet shamelessly magnify it, so that at least to the wretched satisfaction of his own follow he suppresses and evades the truth.” 
Argument from authority is a classical fallacy. It is not because authorities are necessarily wrong, and so no one should look to what a particular authority has to say, but rather, the argument of any particular authority should be examined on its own merits. Authorities can help us because they should have considerable knowledge and wisdom on those subjects they have studied, but, nonetheless, we must recognize authorities nonetheless are fallible. We must ascertain the value of what they say. Those who have good records on particular issues are worth listening to, but the truth of what they say does not come from them and their authority, but the truth itself. Thus, presenting what authorities say is in itself not an argument from authority, but saying that they are authorities and so what they say is necessarily true, is, and when people listen to such arguments, they can be and are easily led to error.
Custom leads to error because the promotion of custom tells us to accept tradition, whether or not what such tradition says is good or true. This is another typical fallacy, appeal to tradition, however, invoking custom can be seen as a special form of argument from authority, with custom being that authority. Custom, tradition, can be hard to overcome, because those who question custom will find themselves in opposition to those who promote and defend tradition and assert that because it is a long-established tradition, it must be true. There is value in tradition, but it needs to be constantly examined; just conserving the ways things are allows the evils which exist to continue to exist. As with all other errors, the argument against a particular custom or tradition must be made in a way which demonstrates the error of that custom instead of just making an assertion that such tradition is wrong, because of course, custom can be correct, and opposing tradition itself can also create and lead to error if the only reason why one opposes traditions is the desire to change things. Change can be good, but it has to be the right kind of change.
Similar to errors arising from custom, errors arising from popular prejudice are difficult to overcome, because what is being rejected is commonly held belief. Traditionally, this fallacy is called argumentum ad populum, that is, an appeal to the people (or the bandwagon fallacy). Like appeal to custom, it is also a kind of appeal to authority, with the authority being the beliefs of the people involved.
Both custom and popular opinion, likewise, have a tendency to justify themselves through circular reasoning. Thus, the argument goes from they would not be believed if they were not true, to they are true because they are believed and put into long-standing practice.
What is worse than the first three kind of errors, because these errors try to employ some level of knowledge, is the fourth kind, where ignorance asserts itself as knowledge and creates, as it were, all kinds of arguments based upon that ignorance, adding ignorance to ignorance, leading to worse and worse errors. Those engaging the first three kind of errors at least try to employ some level of knowledge and wisdom, either from experts who have made mistakes, or from custom and popular common opinion, acknowledging therefore the need for external verification of one’s beliefs, while the fourth ends up not requiring or allowing any such verification. The first three arguments allow for some level of humility, while the fourth employs pride as a support for ignorance. So long as someone is so attached to themselves and their own ignorance, they will be unwilling to reach out beyond themselves and learn what is necessary.
All four obstacles, of course, can and often do work together. One who is ignorant, and prideful in their ignorance, might still try to employ authorities to justify their beliefs, when they can find them. It is not because they rely upon authorities to establish their beliefs, but rather, they establish their beliefs and then pick and choose authorities which they think can and will serve them in promoting those beliefs. We can see this in the way many fight against vaccinations. They absolutely deny the good of vaccines, create false assertions, such as vaccines causes autism, and despite science proving them wrong, they go back and use various “authorities” to promote their claims (such as Andrew Wakefield). They think classical, pre-modern, medical practices are enough to deal with dangerous pandemics, ignoring the fact that vaccines have saved countless people from diseases which were otherwise out of control for centuries.
Thus, Bacon, understanding this, continued:
But, still worse, men blinded in the fog of these four errors do not perceive their own ignorance, but with every precaution cloak and defend it so as not to find a remedy; and worse of all, although there are in the densest shadows of error, they think that they are in the full light of truth. For these reasons they reckon that truths most firmly established are at the extreme limits of falsehood, that our greatest blessings are of no moment, and our chief interests possess neither weight nor value. On the contrary, they proclaim what is most false, praise what is worst, extol what is most vile, blind to every gleam of wisdom and scorning what they can obtain with great ease. In excess of their follow the expand their utmost efforts, consume much time, pour out large expenditures on matters of little or no use and of now merit in the judgment of a wise man. Hence it is necessary that the violence and banefulness of these four causes of all evils should be recognized in the beginning and rebuked and banished far from the consideration of science.
It is important to understand what leads to error; it would be helpful if we trained people to know what the most common fallacies are and why they are wrong. Fallacies are bad arguments (and so, mere opinions, though erroneous, are not fallacies, because opinions are not arguments, but when arguments are made from such opinions, since they are arguments, can designated as fallacious). It is important for us to realize the limits of human reason, so as to know how and why even good authorities are limited in what they can offer, while on the other hand, it is important to recognize the value of reason so as to make sure that good arguments are made to promote the truth and make sure we do not rely upon opinions which are established without any good rationale. Humility is needed: we should not rely exclusively on others, nor on ourselves, but it is better to rely upon others, be it some expert, tradition, or popular opinion, than it is to rely upon our own ignorance and bravado based upon that ignorance. When we begin to trust the arguments from others, we already begin the journey outside ourselves and our ignorance, and then those errors can be slowly overturned in the fashion Bacon suggested: “There is no remedy against these three evils unless with all courage we prefer strong authorities to weak ones, reason to custom, the opinions of the wise to popular prejudice…” We need good authorities, those who are exceptionally knowledgeable in the areas being discussed, who can provide evidence for and prove, as much as any authority can prove, their assertions, in ways which no one can properly counter. We need to promote reason, teaching people how to think, and the various ways we can be mistaken if we reason incorrectly, so that we do not find ourselves blindly led by custom.
We have seen the dangers of these obstacles to knowledge in the way various conspiracy theories have spread among us. QAnon, for example, engages popular prejudice and arguments from bad, indeed, untrustworthy authorities. It leads people astray, using people’s prejudices to do so. This is why, no matter how often QAnon is shown to be wrong, it becomes difficult if not impossible to change the beliefs of its adherents. They want their beliefs to be true. They want easy explanations for why things seem to be changing contrary to their desires. They want their ignorant ideas to be spread far and wide, and they want to control society based upon that ignorance; it should be no surprise, then, no rational argument can be made against them which they will believe, for their ignorance blinds them from accepting evidence to the contrary. It is also no surprise that members of QAnon, likewise, rejecting the validity of the recent American election, have caused insurrection, with the invasion of the Capitol, the people hurt and killed, and the people who would be hurt and killed if QAnon and their supporters had their way, representing the dangers which come out of the acceptance of such ignorance.
Roger Bacon’s observations can tell us much of our own day, and the way various errors are being spread far and wide. He understood the subtle way ignorance works and the harm it can and will cause to society when it is not confronted and put to an end. Reason combined with experience, the acceptance of credible authorities who demonstrate what they claim instead of weak authorities who show ignorance of the subject matter at hand, and the elimination of popular prejudices which reinforce bad ideologies and the habits which come out of those ideologies, are what we need today. But, due to pride, and willful ignorance among so many, it is clear that the work ahead of us is not going to be easy. However, it is possible. There is hope. The truth is stronger than lies. No matter how many people try to resist it, the truth will continue to be there, presenting itself, until at last, its challenge to error is uncontestable. History has shown us this many times. It is not easy, but progress can be made, because it has been made before. We are currently at a time of crisis, where education has been undermined, and ignorance has shown its corrupting influence over society; the harm which this has done is obvious; the question is whether or not we have the willpower to change our ways, to deal with the situation at hand, or if error will continue to run rampant and take greater hold of society, creating even worse problems for us to confront. How we deal with the present crisis is up to us. We must come together. We must work together. We must work to repair the harm that ignorance has done to society. We must acknowledge our own mistakes, and do what we can to fix whatever damage we have done through them, and in doing so, we must welcome others who see through the fog of ignorance and now see the truth. After all, history shows, this is also how progress is made.
 Roger Bacon, Opus Majus. Part I. trans. Robert Belle Burke (Philadelphia: University of Pennsylvania Press, 1928), 4.
 Roger Bacon, Opus Majus. Part I, 4.
 Roger Bacon, Opus Majus. Part I., 4-5.
 Roger Bacon, Opus Majus. Part I., 19.