I heard it in this particular phrasing after I'd already learned it the hard way.

That hellish boss who's constantly undermining your efforts to do good work? She's afraid of losing her job, and incapable of dealing with it like an adult. That "friend" who starts spreading rumors about your lack of fidelity? She likes your boyfriend more than you. That roommate who leaves her still-milky cereal bowl on the coffee table for a week? She's busy and inattentive, and her parents never taught her how to keep her living space tidy.

You can be the most upright, considerate citizen in the world, and still these people will do these things. So stop taking it so personally and find a way to live with it, make it livable, or move on with your life.