As a mature adult, you are expected to be patient, kind, understanding, generous, forebearing, tolerant. You're supposed to be the epitome of good manners and right conduct. But sometimes, what you really want to do is cut loose--to yell, cry, accuse, berate and insult. You want to get things off your chest. You want to tell people exactly what you think of them. But you can't. That's not done because what seems to be paramount is the preservation of harmonious interpersonal relationships (at least from the outside). The ugly truth is best kept hidden. Is this what maturity is about--keeping a veneer?
While in the best of all possible worlds maturity is supposed to mean a change in what you think or how you feel about something, I sometimes think that people will settle for greater skill at hiding it.