It's hard to admit you did something wrong because of what it implies.
Am I stupid? Am I not as skilled as I think I am? Did I miss something? Perhaps all of the above?
I think this is hard for smart/perfectionist people because we think we should get things right, and this is likely to be tied to our ego/identity.
But I've come to the conclusion that humans are just fundamentally stupid, because even extremely intelligent people fuck things up all the time.
Not sure if it's the right thing to conclude from my observations, but it does make failure easier to deal with since I can remind myself that yep, I'm still just a dumb ape.