The sad part is that when coaches overemphasize not making mistakes, they often create the fear in their quarterbacks. Coaches can ruin the processing a quarterback makes on the field. As a QB, you are trained to learn the offense. You memorize all the formations and route progressions. The progressions are based on the reads of the defense after any adjustments are called at the line. In other words, the security is already built in with all the presnap reads, and you follow the progressions in order based on what you see and who is open.
When a QB is drilled over and over to be careful, or what not to do or where to go with the ball...it's like adding internet security to a computer with a different set of parameters....except the QB's mind is the computer and it gets bogged down and confused. It slows everything down and CREATES doubt. It can be debilitating to a quarterback and is almost always counterproductive.
Obviously, everyone is affected differently, but I believe Trubisky is paralyzed by what they are asking of him, and the parts of the playbook they are taking away from him.
Much of this is still on the QB. A quarterback needs the self confidence to execute what is asked of him, but coaches need to put players in a position to succeed. The should be tailoring the offense to the strengths of the QB that is playing. It appears that they are not.
Either tailor the offense to the starting QB, or put a QB in the game that can perform under the parameters set forth.