I heard this often from my therapists, when I was upset that I did not do better during therapy: "You did the best you could."
Or when upset at parents' emotional abuse: "They did the best they could."
Or when I complained about a person who constantly had money trouble and was affecting me: "She did the best she could."

This is a double-edged sword: It's both comforting to know or think that people always do their best, but also seems to pretty much make any behavior seem like the best anybody could do and beyond reproach. I mean is there literally any behavior that we can mention and the therapist would say, "No, that was far from the best she could do, she was being lazy, irresponsible, selfish....? My therapists have never said that. Though they've admitted some behavior upset me or harmed me, it has always been "the best they could do."

edit: I just thought of something, what if the "best they could do" is not the same as the "best they can do"? And how do you encourage somebody to be the best they can actually be?