When the Dallas Mavericks decided to trade away Robert Traylor for Dirk Nowitzki in 1998, they thought the big German had high potential. It is highly unlikely anyone saw this career coming, though. Dirk accomplished a ton including a regular season and Finals MVP, top five in career scoring, and 21 seasons with one franchise, something that will probably never happen again.
There is nothing wrong with players changing teams. In fact, sometimes they should. The NBA is different from other leagues. The narrative of a basketball player’s career is much more important than a football or baseball player’s.