You're assuming everyone does. I "pay for performance" and my tips will generally bottom out at 10% (I feel a cad not tipping at all, though I shouldn't) and max out at 50% (very, very uncommon and usually requires my creating extra work for the server, such as breaking a glass/ spilling a drink on the floor).
Re:Observations from a Tipless Restaurant
by ryanbrunner on Tuesday July 30, 2013 @12:59PM
(#6128287)
But even then, you're clearly not 100% motivated to "pay for performance". To some degree you are, clearly - but a large part of why you tip is cultural expectations, or you wouldn't be tipping 10% for horrendous service.
Which is fine, I'd never not tip in Canada or the US either, but let's be honest with ourselves - everyone tips because you're culturally expected to tip.
If you honestly tip to reward good performance, why are you rewarding horrible performance at nearly the rate that you reward excellent performance?