A friend of mine recently told me that he gave his notice to leave the company. We work for the same company, and he is the one who referred me originally. I was surprised when he told me, but after he explained his reasoning it made sense. Our jobs as consultants require us to travel, and this no longer works for him and his family responsibilities.
This week I started a new assignment with a new client. In some sense it's like starting a new job. Even though I am employed by the same company, everything else changes from one assignment to the next. Assignments eventually end, and I actually like this forced change because it keeps things interesting. The longer you remain in the same position, the more inertia there is to overcome to move to another position (unless things get unbearable).
When you start a new job, most likely you are not thinking about leaving that job. But you should be. You need to avoid burnout. You need to leave a job long before it becomes unbearable.
The moment you start a new job you should draft your resignation letter and this article explains why.