I believe that when working on a job, for those who will never fall into the first category which is, being layed off due to incompetence on the workers part. Is as much as you're employed and also doing your best on the job. Maximally, one should really not wait till anything starts to happen before looking for another job. Most of us gets a job and stays convenient working there for years. As time goes on one will become obsolete because they ain't going out of a particular organisation to see what others are doing...

Now take for instance you get a job and after working on it for 2 years, you start to look for better offers from other companies as regards the job you do. You won't only gather experience from all round. You'll also move out of a place before they start to feel like they've seen it all from you, and also you get better offers proving that you make sure you learn every single times you're in a new place and also know how to apply those things...

A water that stays on a spot for long will start to stink, while the on that flows will stay fresh