You have a 1 in 20 chance of being chosen by YC. Pretty good odds!
https://news.ycombinator.com/item?id=47549If we assume there will be 500 applications and that YC will be accepting 25 of them then that's a 1 in 20 chance.
Throw in the fact some applications, maybe as many as half, are broken (thirteen year old founders, clones of existing ideas, etc) and you've got a great shot.
Anyone that still has cold feet, get in there and apply!