I have found that it is very simple. If on late Sunday afternoon you start to get a feeling of dread in your gut because you have to go to work on Monday morning you are not happy and there are better things that you could be spending your life doing.
Yes. Then pesky things like a mortgage and bills get in the way and you have to decide: Shall I live or shall I live?
I don't think Marcus is suggesting that you shouldn't work, but that you should find a way to do something you don't hate doing. Are you really living if you spend half of your waking hours being miserable?
I grossed more money working my way through school than I make now, but I'm comfortable and infinitely more happy.