[healthyhippo]

The psychological impact of being wrong is big enough to do it very often. Everyone going "oooooh... AHH" when they show the slow-motion ball cam, and most of the time its out.

Then everyone looks at you like you're the asshole. All of a sudden you're vilified, and home court advantage can shift over. There's little to be gained unless it was truly very close and the call went against you.