What makes the difference between “Hire” and an honest “almost” for final on-site interviews? [closed]

Question

So, I have recently had on-site interviews with Google and Amazon and received polite rejection letters letting me know I was close, but not quite right for the skills they were looking for.

I've made it to the final round for all the interviews I've done (except for some offers from small uninteresting positions that I interviewed with for practice), but so far having 5-8 interviews in a day gives me enough time to have my mistakes add up just enough to put me out of the running.

I know I did well there at least on the coding questions and other general technical questions, apparently I'm bad at designing OOP things like card games or parking garages though (I dove too deep into one object and used up all my time, instead of being broader) and my coding answers although they work overall didn't quite had a few bugs/edge cases I missed (like a case where an input node could actually could be the answer rather than needing to be distinct). And I have no problem saying "I don't know", but maybe I'm rambling a bit and need to say it for questions I think I can answer, but can't give a crisp answer to...

So, what are the things that push you over the top from being good, but not quite to "Hire"?

Any advise on what you look for or something you know that gave you that little extra boost?