Last week I visited South Carolina to see a couple colleges and was reminded of high school students seeking to get into certain colleges and basing their own sense of self-worth on those admittances. I'm not sure if anxiety about admissions is any greater or lesser than it has been in the past, but from my perspective, many students are putting themselves through a lot of unnecessary, albeit understandable, stress.
Some anxiety is good as it causes us to perform at a higher level and stay on top of our work, but too much stress is counterproductive as it leads to poor performance and burnout. Such negative anxiety partially arises from seeing one's worth through achievement and even more so when the arbiter of that achievement is external, as is the case with college admissions. Anxiety would remain at a productive level if students saw the process as a sort of game in which they would like to do well purely for the sake of doing so. Since falling short is no comment on self-worth, it is not to be feared to any damaging degree.
Such a mindset reminds me of Carol Dweck's approach to learning. (If you don't know about that approach, you can read about it here: https://mindsetonline.com). Essentially, a growth mindset sees failure as a learning experience. I would go a step further and be sure to define failure. Not getting into a college with a 20% admittance rate is not failure. Failure would be more like not answering a math question correctly or having logical errors in an argument; it can be objectively agreed upon as an error or failure. College admissions fails that test as the arbiters have to base their decisions on factors - standardized test scores, recommendations, essays - that point to success but can't completely and objectively assess it. Admissions staff also have to take into account institutional needs - for example, finances or athletics - that sometimes mean a denial for a student who doesn't fit that need but might otherwise merit a spot.
Though difficult to accomplish, seventeen year-olds shouldn't base their self-worth on these admissions decisions. And, if they don't, the productive anxiety level would, paradoxically, help them take chances, learn more, and continue to perform and understand at higher and higher levels.