The annual college applications frenzy is upon us — a season when high school students agonize over G.P.A.s and personal essays, hoping and praying that they will stand out among throngs of applicants.

The anxiety among applicants about how to present themselves to universities is very visible online. Websites have sprung up to advise students on, say, whether teacher recommendations make a difference or whether to write about money in a college essay. One website, College Confidential, has offered a seminar in which you “learn what admission officials discuss behind closed doors” but “may not tell you in the information session.” Desperate applicants ask other site visitors — complete strangers — to “chance” them, or estimate the likelihood they will be admitted to their dream college.

This degree of bewilderment is troubling, but not surprising.

Colleges themselves have widely diverging views on what makes an ideal applicant. It’s a widespread misconception that applicants have an automatic right to be admitted to the school of their choice if they have higher grades or test scores than other candidates. It’s not that grades and test scores don’t matter — they nearly always do — but colleges aren’t obligated to choose the students who are deemed most likely to earn high college grades or graduate. As the legal scholar Ronald Dworkin put it, there is “no combination of abilities and skills and traits that constitutes ‘merit’ in the abstract.”

Instead, what counts in admissions depends on the mission of the institution — and that can vary a great deal from school to school. The State University of New York, for example, strives to “provide to the people of New York educational services of the highest quality, with the broadest possible access, fully representative of all segments of the population.” Yale’s mission, on the other hand, is “to seek exceptionally promising students of all backgrounds” and “to educate them, through mental discipline and social experience, to develop their intellectual, moral, civic and creative capacities to the fullest.”