Being an NBA general manager is hard. Sometimes, the moves you make that seem like obvious wins at the time don't work out. Unfortunately for Sean Marks and the Brooklyn Nets, that's exactly what happened with Terance Mann. The Nets took on Mann's contract in a trade last Summer, also acquiring a first-round pick that turned into Drake Powell. While getting the pick was the sweet part of the deal, there was hope that Mann could be a veteran leader in the locker room. Maybe even that he would play well enough to fetch a draft pick at the trade deadline. As everyone now knows, things didn't quite break that way for Brooklyn. Mann appeared in 63 games for the Nets last season, third most on the team. He made 51 starts, the fourth most on the roster. Despite all of those games, he never settled in and found a rhythm. Mann averaged just 7.2 points, 3.2 rebounds, and 3.0 assists in just over 24 minutes per game. He shot a career-low 45.7% from the field.…