Criticism — being mean, in a sense — can be fun. We seem to show off a bit of our mental acumen. “Good one!” people cheer on when someone makes a particularly wittily barbed comment. It’s what “the dozens” is all about. So giving up that potential scoring comment is a form of self-denial — a big idea in Catholicism.
Faber explains it better:
The practice of kind thoughts also tells most decisively on our spiritual life. It leads to great self-denial about our talents and influence. Criticism is an element in our reputation and an item in our influence. We partly attract persons to us by it. We partly push principles by means of it. The practice of kind thoughts commits us to the surrender of all this. It makes us, again and again in life, sacrifice successes at the moment they are within reach. Our conduct becomes a perpetual voluntary forfeiture of little triumphs, the necessary result of which is a very hidden life.
That seems to be a good definition of magnanimity.
The quoted excerpt is from Father Frederick Faber’s Spiritual Conferences, excerpted here.