I'm sure Danny Ainge has made promises to players. I think sometimes promises are part of a reason why you see a guy slipping farther than you think he should.
If you thought you'd have a pick of players q thru z, but didn't think you could pick a player a thru p, you'd make a promise to one of the players in your range, so they wouldn't work out or interview with other teams in your range, helping the odds that they drop to you.
But, if you make that promise to Arm Tellum, a powerful agent, even if a player from that more talented a thru p range drops to you, you're better off honoring your promise.
I think this happens a lot.