For an example of why: my startup was initially rejected from Startup School, then accidentally accepted, and then we kicked butt and won the YC Startup School Grant out of 10,000+ startups. Then we got a YC interview and were rejected for what (I think objectively) was a pretty random reason. And I understand that the stated reason isn't necessarily the full reason.
It was still a very enjoyable and super helpful experience overall. The advice, $10k cash, and cloud credits have helped tremendously and it's still helping a lot.
I just wish I could have competed against other startups for acceptance into the core YC program, rather than have a few people attempt to judge how much of an "animal" I am in 10 minutes as they groggily try to wake themselves up with coffee. Not a knock against them at all (still a very long-term PB fan!), just the process.
Because I know I'm much better at competing with hard sustained effort over the long-term than I am at seeming super impressive on first impression.
Anyway, that's my suggestion.
We will hopefully be ramen profitable soon, and may not try for YC again because it is mentally exhausting. But whatever we do, Startup School was a huge boost for us and YC asked nothing in return, so thank you very, very much.