Benedict Cary has a nice piece in the Tuesday Science NYTimes section
...genuine excuse artisans — and there are millions of them — don’t wait until after choking to practice their craft. They hobble themselves, in earnest, before pursuing a goal or delivering a performance. Their excuses come preattached: I never went to class. I was hung over at the interview. I had no idea what the college application required...The urge goes well beyond a mere lowering of expectations, and it has more to do with protecting self-image than with psychological conflicts rooted in early development, in the Freudian sense...As a short-term strategy, self-handicapping is often no more than an exercise in self-delusion. Studies of college students have found that habitual handicappers — who skip a lot of classes; who miss deadlines; who don’t buy the textbook — tend to rate themselves in the top 10 percent of the class, though their grades slouch between C and D...The important thing for some is, no matter the method, to avoid considering the alternative explanation...as in the Marlon Brando line from "On the Waterfront": "I coulda been a contender."