The first “not good” thing in the Bible is Adam’s isolation and aloneness (Genesis 2:18). It’s the one discordant “not good” in a string of “goods” that ends with a “very good.”
Later, Jethro tells Moses that spending his day judging the people without any help is “not good” (Exodus 18:17). Moses needs “helpers suitable to him” in the judicial sphere, as Adam needed a liturgical partner in the garden sanctuary.
What’s not good is that Israel walks alone, impervious to correction from God or man. No one speaks, no one rebukes, no one tries to redirect. They have become dull of hearing, and without open ears they are alone on their dangerous path. They are perfectly content, alone with their own thoughts.
Political, moral, marital goodness requires otherness and relation. It is not good to be alone.