One of the stupidest clichés I've ever heard in my life is "you shouldn't hold grudges".
I actually believe it's GOOD to hold some grudges.
Grudges are a reminder that the other person is psychologically dangerous to your mental health, and is a danger to anyone who comes across them!
I even go as far as saying that not holding grudges is dangerously naïve and makes you even more vulnerable to psychological war games used against you!
So if someone wronged you on purpose and refuse to make a sincere apology, then hold that grudge without shame and be proud of the grudge that you're holding!
