I think the biggest reason for leaving a job is when the company you are working for changes. When new management comes in they usually want their own people. Plus they will now do things their way, not the way you have been used to. That in itself may not be bad, but if it is not something you can work with or adapt to, it is a time to change. Staying for the sake of staying is not good. Nor is leaving at the smallest unsettling thing. You do have to carefully think about what it is you really want. Then act appropriately. Out of the frying pan and into the fire was never more true.