In 1965 Elliot Jaques introduced the phrase 'mid-life crisis' to the general populace. It described a phase in life where people became generally unhappy with all of the things that they've achieved and adopted often destructive behaviours in an attempt to recapture their youth.
It can be a very dangerous or an empowering thing depending on whether or not the individual recognizes the signs. Here are a few signs and things you can do.
You've spent years working your way up the ladder and now you have a job that pays well and perhaps even bores you. You want to quit and find something new, something refreshing and challenging. Stop right there. Don't forget how long it took you to get this far. If you can make a move workwise that will give you more challenge and more pay then this is okay, but don't take a pay cut just to get something new for a brief space.