For example, Mourihno is known to be a tough coach who takes no nonsense from players, but when he wasn't playing Kevin, and Kev believed he deserved to be played, Kevin said "I'm out." Why coz Kevin's talent and Perception of his talent told him he was better off without Mourihno. Kev backed himself and today it's hard to say he was wrong.
Had he towed the line, and become a backup or "stay and prove to the manager he is worthy" as many pundits like to bleat, I doubt he'd have become the worldy he is with us today.
Funny enough the very same was the case for Yaya at Barca, pigeonholed into a DM role and asked to stay and backup Busquet. He too like Kev said no, came to us and became one of the most dominant CMs here. Had he too towed the line, and stayed as a backup at Barca, he's time and worth would have been diminished. And he'd have never achieved the individual accomplishments he did here.
True managers have to consider the team overall and over any player. And axe, demote, reprimand and oust those who don't fit for one reason or another, but in the same vein, players who "back themselves" will do the same. If it's not working here or even id it is and you believe there is something better, reach for it. It is only those who try that achieve greatness.
If your manager or club doesn't rate you as highly as you think they should, back yourself and go find a manager and team that will. The fans will boo you, but your new fans will celebrate you when you deliver. And there is nothing wrong with either position, if we are being honest that is. :-)