I'm fortunate enough to have been included in that 5.7% today. Nonetheless, the statistic is highly misleading and the entire college process is becoming increasingly arbitrary. With so many talented candidates, it is often simply a crapshoot for all but the very best applicants.

Admission to an individual school in particular is extremely difficult to predict. I have friends who were just accepted to Harvard and rejected from Stanford, vice versa, accepted to Yale and neither Harvard nor Stanford, etc. It's similar to an earlier discussion today here on HN about the applicability of group statistics to an individual situation: even if you're an exceedingly qualified applicant, your essays just might not click with a particular school's screener. Or perhaps you're not fully qualified, but someone in the admissions committee really connects with your personal story. These kinds of things happen all of the time in college admissions; with such a competitive pool, getting into any particular school often comes down to chance.

As for the acceptance rate itself, it's as much a measure of how good a school is at marketing as it is of its competitiveness. Harvard (and many others) sends pamphlets by the thousands trying to bait almost-certainly-hopeless students into sending an application, just to drive down their acceptance percentage. Many schools also reject candidates that are "too good," ("Tufts syndrome") because an admissions office will gamble that such candidates will matriculate at a better school. They would prefer to get their acceptance percentage lower than accept a student who probably wouldn't matriculate.