Here is the importance a veteran has on a football team

Since then multiple athletes have spoken out with their opinions on the matter.
Some, like Sean Salisbury, agree with him:

While others, like Rod Woodson and Kurt Warner, disagree.

So what's the answer? The Bears brought in Trevor Siemian for the purpose of helping Justin Fields grow. They have actually made a pretty steady habit of it. Trevor Siemian, Andy Dalton, Nick Foles, Mark Sanchez, and Kordell Stewart just to name a few. Some were signed for the purpose of holding a clipboard and being the training wheels for a young quarterback. But some, like Andy Dalton and Nick Foles, were starters, and then not, and then again. It's hard to say what their jobs were. Who knows where Trubisky could have been if he had someone other than Mike Glennon as his mentor.

None of the quarterbacks that the Bears have signed have said that it was not their job to mentor. Is it because Tannehill is afraid of becoming the next Brett Favre or Drew Bledsoe? All it would take is one week where he can't play. Then Willis shows talent and from then on Tannehill doesn't have a starting job. The problem is, that everyone is replaceable. It's not just in the NFL, but it's hard to find a job where it's as obvious as in the NFL. Favre had Rodgers, Bledsoe had Brady, Manning had Luck, and everyone has a replacement. Are the replacements always going to be the same level or better? Definitely not. But can they do the job well enough to win games? Most of the time, the answer is yes. And in most cases for much less money.

So does that mean that every starter should mentor their successor? As Sean Salisbury said, it's not in anyone's contract that your first priority is teaching the second string. But being a good role model is. Tannehill mentioned if Willis watches him and learns something, good for him but Tannehill is not helping him out in the film room or at practice. Look at Peanut coming back and talking to this year's Bears. Giving them advice on how to be successful.

If it isn't obvious already, I have to side with Warner and Woodson. Tannehill doesn't have to go out of his way to show Willis the ropes. But if Willis has a question in film or asks for a spot in practice, what kind of a guy straight up says no? The kind of guy who doesn't want his team to grow and develop. The coaching staff is there to lay the ground rules and show you what they want from their team. Teammates are there to help each other achieve those goals. Dalton and Foles did it without grief and Poles has brought on enough support to help fields grow.

So should a starter have to train the 2nd string? No. Should a teammate help out another teammate? Every time they can.