Agreed with Lexie: while learning to accept that things aren't fair is a valuable, important part of life, there's a difference between letting frustration overcome you and channeling it toward a constructive purpose. If we all shrugged off bad things as "the way they are," no progress of any kind would be made. Recognizing that things aren't as they should be can lead to meaningful improvement.
It can also lead you to dissociate yourself from negative/parasitic environments. Sometimes the only thing you can do is step away from a situation.