I can speak from experience … well of a sort…
We had an obnoxious lad here in the village, first met him when he was about 5…he grew into a troublesome teenager, big chip on shoulder… etc etc…then he moved on to who knows where.
WELL… after a couple of years, he paid a visit to his old haunts. What a change…he was chirpy but polite, smiling etc etc. It was a pleasure to chat with him…and he even sorted out a youngster who was about to do wreck the flowerbeds… 
Turned out, he had joined the Army some months before… and… all I can say is… thank heaven for that.