So i was just wondering something, i was talking to a person i met about bottom brackets, and he told me that on campagnolo cranks you have to have a campagnolo bottom bracket and the same goes for shimano,

why is this, shouldn't parts fit standard?

and the bottom bracket i have is a square taper shimano, i have an extra pretty good condition campagnolo crank that i want to put on the bike, but i haven't yet because of what he said