Yeah, that argument hasn't worked well for me. I remember not holding a grudge against a business partner I'd had who had gone off with my laptop a couple of years before - and then he stole $1000 from me.

Grudges against living people remind you that they are criminals, liar, crooks, cheaters or whatever other bad thing they did to you.

The lesson is this - you shouldn't keep grudges for petty little things. But if someone consciously fucked you over, don't forget it.