For a rational actor, it should be an unstable equilibrium. If you can make more profit per hour spent in your spare time that in your job, then it won't be lo

For a rational actor, it should be an unstable equilibrium. If you can make more profit per hour spent in your spare time that in your job, then it won't be long until you quit and spend all of you time. If not then you will give it up, unless it is just a hobby. (Hobbies might be exception to the rule)