The problem that strikes fear in the hearts of many applicants is how to assess their chances. Especially at selective schools, this issue can be dicy. I recommend that students get a copy of the college's student profile that includes SAT ranges, average high school class rank, percent accepted, etc. If you fit the average profile at a college that accepts more than half of its applicants, you'll probably get in. If you don't need financial aid, the odds will be very much in your favor.
For colleges that accept less than half, you'll need to be above the profile averages to have a 50/50 chance. A college that accepts 20 percent may deny hundreds of applicants with scores and grades above its averages. Most Ivy League schools could choose an additional class of freshmen from the deny pile that would have scores just as high as the ones who get in. Many people mistakenly think that the goal of a highly selective admissions office is to assemble a class of the best students available. Its real purpose is to choose an academically able class with a diversity of talents and backgrounds.
The student profile at the Princetons and Northwesterns of the world would be intimidating to anyone. But once you get past the elite, many colleges rig the numbers to make themselves look more selective than they really are. I'm not suggesting that they lie, exactly, but their creativity with statistics is second only to that of presidential candidates.
Assessing your chances for admission is a ticklish process. You must avoid overconfidence yet not succumb to the I'll-never-get-in-because-I'm-the-dumbest-person-in-the-class syndrome. When in doubt, hedge your bets.