The problem with Mignolet is that after he's dropped, he would bounce back when given the opportunity, which is good. And all would appear fine and we would have a very good keeper for half a season or so. But then the next season, errors would creep in into his performances again. We would drop points due to his errors. A winning game becomes a draw game. A draw game becomes a loss, etc, etc. He would then have a crisis of confidence and perform worse until the manager has to drop him again. This cycle has happened 2 times during his time here and under 2 different managers.
What he needs to work on is when he makes an error in one game, he needs to bounce back quickly the next game. No world class keeper has a season without errors. The difference between him and world class keepers is that world class keepers soon forget their errors and bounce back right away.