Why do large raids suck?

It's quite simple, really. Here's the formula:

ir = (pe ^ 2) / 2 + (pe-1)*3

where

ir = Chance of irritation
pe = Number of people

This is graphically illustrated to the right.

You can see that the chances of significant irritation in a 5 man are rather low (20%), much higher in a 10 man (67.5%) and are guaranteed to hit 100% long before you hit the 25 man cap.

Why? The more people you're grouped with, the greater the chance there's some idiot doing something stupid ("ooops, I accidently pulled that next group"). Or inconsiderate ("gotta go for a smoke"). Or both ("ooops, I forgot to repair").

That's why I don't do raids with more than 10 people these days. Waste of good gaming time.