I recalled a scene from
Driving Miss Daisy. At the end of the film, both Hoke and Daisy are quite old. He visits her in her senior home. They have this exchange.
Daisy: How are you?
Hoke: Oh... I'm doin' the best I can.
Daisy: (laughs) Me too.
Hoke: Well, I reckon that's 'bout all there is to it then.
The best we can do is all we can do. To me that's what not being bitter means. It means doing our best. Being bitter is a kind of giving up, a kind of quitting. It's hurting yourself to spite your circumstances or those who have hurt you.
That said, seeking justice is not necessarily being bitter.