Tatum and Brown have to learn to keep playing through disappointing swings and individual plays that don't go their way.
Also, they are on a team that's supposed to be a title contender, and so when things go well they are getting too happy. Stop with the celebrations after made three pointers and dunks (even it's just a momentary mental celebration). Stop getting so high when there's a good or great play. Stay grounded and keep playing through the good and bad, until the game is in hand.
No more stare downs after a dunk, which is a waste of energy and just motivates the other team. Even Al has been doing this. Cut the macho crap you're the Celtics. Just run back and play defense and rest and celebrate when the other team has been put away.
Let Morris be the trash talker, enforcer, guy who stares... other players shouldn't be emulating him. I like that about Kyrie. He makes a great play and acts like it's natural and doesn't show up the other team... That approach should be emulated by everyone on the team not named Marcus Morris, who is just being himself when he does it. One Mook per team is perfect.