Colleges are like any other organization, corporation, or government institute. They have a mission, vision, board, targets, and many are even for profit. Mission and vision tend to all focus on the core goal of spreading education, research, and grooming the brightest minds. There is a misnomer that the best institutes look for the best minds identified through school marks or achieving results akin to a child Steve Jobs or Tiger Woods. Although there is some truth to this, majority of admissions is not based on this.
Unless a college admission is solely focused on a cut off mark, any college speaking about holistic admissions process is almost always looking for students that are able to fulfill the following -
Will the student add to to the diversity of the student body, in terms of thought process, activities and more. Such colleges talk about multi-subject holistic learning, so it is but obvious that they seek the same in their student body as a whole. This is the reason why every Harvard student doesn't have 1600 on his SAT.
Does the student abide by the values that the college stands for. Values of a college, like any organization will sometimes be explicit but more often than not, it is implicit. It is known to the admissions officers and they can pick it out from an application. It is very important because like in a company, if values are aligned then it is much easier for progress to expedite itself.
Does the student have the right characteristics, giving the university confidence to allow him or her to use their brand. A college plans to be around much longer than the 3 or 4 years a student attends the same, and so focuses a lot on its brand. One effectively procures the right to use the college brand to leverage their career. I use University of Michigan, every time. The brand stands for certain values and the college wants to know is it going to be used by the right person. No one wants their name to be tarnished by the deeds of one student.
Once one understands the above points, they will know the admissions is no longer about marks, activities, and certificates. If you are able to look at yourself and your application from the standpoint of the university, you will be easily able to -
1) Answer if you are the right candidate or applicant
2) Is the university right for you to succeed (don't succumb to shiny brands)
3) What you should put in your application and how you should put it
After all of this, it does come down to the final chance during the review of your application, and sometimes the timing of it all. Don't beat yourself too much also.
Disclaimer- With all institutes there will likely be some threshold of achievement or standing, below which they will not admit anyone unless it is very well compensated in another field (it reflects low level of commitment and dedication to succeed).