Well, I got a reject as well. Last time a few years ago, I'd actually got a call for interview and personally, if I've to judge the two ideas on merit, the current one was way more superior than the one that got an interview call(eventually we didn't get funding but we were very very under-prepared back then).
My key takeaway is - there's no 'right or wrong' here, it's kind of random. It's got a lot to do with your luck.
So what YC says in their rejection letter is actually right, we can always cook up reasons, why one got rejecte. The only way to make sure (well not really, just making it highly probable) that you make it to YC is be extremely well prepared, but then you are probably beyond a point where you need to go to YC.
My key takeaway is - there's no 'right or wrong' here, it's kind of random. It's got a lot to do with your luck.
So what YC says in their rejection letter is actually right, we can always cook up reasons, why one got rejecte. The only way to make sure (well not really, just making it highly probable) that you make it to YC is be extremely well prepared, but then you are probably beyond a point where you need to go to YC.