Different kinds of luck, and a different kind of game.
Stanford is small, arbitrary luck in a single play game, where failure usually is not something you can learn from, because you will never apply to Stanford again.
One's startup journey is best thought of as an iterated game, where luck mostly around timing, and you can learn from failure and practice your timing.
In targeting an elite college you are in a lottery with 100s of others for each seat. Of those hundreds a few might actually not be "qualified" but generally there is nothing substantial to distinguish 99% of those who don't get in.
Being chosen or not is a particular kind of small luck- the sort of arbitrary circumstantial occurrance that is not under your control and is not something you can learn from. Not "getting in" is not failure, unless you think not meeting the demands of your ego is failure (it isn't).
In starting a business, the range of moves and outcomes, the game board, is SO MUCH LARGER and SO MUCH MORE REAL than anything involved in getting into even an elite college. Here you have other people's money and their livelihoods at stake, not just your own ego. Here success and failure are much more tangible and much more distinguishes between them. Execution is much, much more complicated.
Even among startups who execute well, most still fail because of timing. The ones that succeed also do so largely because of timing. This "luck" around timing is something you can learn.
Said another way- my daughters are used to scoring high 90%s in their academics. Every day I tell them the real world is where the people doing the best are scoring around 5-10%, and of those who do it best the ones who succeed get their 1 right out of 10/20 at just the right time.