Reader Ye Olde Statistician describes the strategy behind such attacks:
“However, to bring down America we do not need to strike big. In such an environment of security phobia that is sweeping America, it is more feasible to stage smaller attacks that involve fewer players and less time to launch and thus we may circumvent the security barriers America has worked so hard to erect. This strategy of attacking the enemy with smaller, but more frequent operations is what some may refer to the strategy of a thousand cuts. The aim is to bleed the enemy to death.”
– the late* Samir Khan, explaining “Operation Hemorrhage,” (Inspire, Nov. 2010)
(*) late: encountered a US missile in the Yemen.
Regarding the cheapness of pressure cooker bombs:
‘In his October 2004 address to the American people, bin Laden noted that the 9/11 attacks cost al Qaeda only a fraction of the damage inflicted upon the United States. “Al Qaeda spent $500,000 on the event,” he said, “while America in the incident and its aftermath lost — according to the lowest estimates — more than $500 billion, meaning that every dollar of al Qaeda defeated a million dollars.”’
In that address, [Adam] Gadahn put his finger on an important insight that AQAP is now reiterating: Even failed attacks can help the jihadists by “bring[ing] major cities to a halt, cost[ing] the enemy billions, and send[ing] his corporations into bankruptcy.” Failed attacks, simply put, can themselves be successes. This is precisely why AQAP devoted an entire issue of Inspire to celebrating terror attempts that killed nobody.
Daveed Gartenstein-Ross, “Death by a Thousand Cuts” (Foreign Policy, November 23, 2010)
Our response to 9/11 was to plunge ourselves into an economically ruinous war. We cannot afford to keep fighting stupid. Because our enemies are not stupid.