There is not a GM in the NFL that has not released a player that later prospered in the NFL.
Some times it is opportunity. Just like in life, some people just can not perform on Tests but know the material in a relaxed atmosphere. In the NFL a test is getting limited opportunities and downs to prove them-self. Once they get the confidence they are the starter they have no pressure and take their performance to new heights.
Some times it is the atmosphere. The coaches philosophy and the attitude in the room. Some players may prosper under a villain of a coach, and not under a players coach.
Sometimes it is slow learners. Some people just do not grasp things quickly and are moved.
Sometimes it is team depth at that position.
Sometimes it is maturity and not all kids mature at the same age level.
Many times it is the system the team plays, and what is expected of that player physically.
It is very complicated.... But no GM is perfect.
""People Will Probably Never Remember What You Said, And May Never Remember What You Did. However, People Will Always Remember How You Made Them Feel."