Al Qaeda's 9/11 attacks were successful in bringing terror and disruption to the United States, mainly because Americans led by GW Bush et al. responded in the least appropriate way, i.e.,
As I said on Sept 12, 2001, the appropriate response would have taken US actions that precipitated the attack into consideration. No such reassessment of alliances, arms sales, covert interventions, etc. ever occurred.
If anything, the attack was wildly successful because it allowed Bush, Cheney, et al. to launch an extravagant campaign of righteousness without facing opposition (or even questioning) from the other branches of government, citizens, the media, etc. They went WAY too far -- and were supported by a number of people who confused their ignorance and righteousness with patriotism and thinking.
The results left the US economically, politically, and morally weaker; see. e.g., this, this, this, and THIS.
I reckon that the US has not just lost a decade (a la Vietnam war) but also its status as "the freest country on Earth" -- a blow from which we may never recover due to increasing competition from other places (a good thing) as well as escalating squabbles among our so-called leaders (a bad thing).
"The first law of holes is that if you are in one, stop digging."
It's no accident that I breathe with relief when returning from the US to the Netherlands, nor that I may live abroad far into the future. (I am still considering retuning to the US to work and perhaps enter politics, but there are costs and benefits to those choices...)
Bottom Line: Stop, sit down and consider why the terrorist attack happened, how we might have better responded, and what we should NOT have done. Hold onto those thoughts, compare your alternative reality to the world we see today and then drive yourself, your community and your leaders to where we SHOULD be.