Well put. The biggest depressive factor in a work environment (to me, at least) is having a feeling of hopelessness, of being "stuck" in a job - even if it's a job you kind of like, being stuck in it makes it much less enjoyable.

You don't even have to quit, but look around, find prospects, prove to yourself that you can find another job if you choose to, and you may find your outlook becomes much brighter. It's a feeling of being in control of your destiny.

And hey, if one of those prospects looks like a more promising path, then all the better.