It happened with Rodgers here. Sometimes players just stop being motivated by the same old voice. I've said it before but except for the rare examples that you've given I think after 3 or 4 years you should be thinking about the next appointment
Brighton do it perfectly, albeit their managers are poached due to how well they do. But unlike us with Brendan, they don't move heaven and earth to keep them as they have a contingency plan already in place