For a long time after a college (you need a college degree to work as a lackey in an office, after all), you will continue to tell yourself that what you’re doing is your “day” job, and not your actual position in life. When others ask you what you do, you will continue to say the thing that you feel you really should be doing, instead of rotely replying, “Office worker.”
After about three to five years doing time in the cubicle, however, you will start to cave to the reality that your dream is now a pipe dream and that your “day” job has become your job (see: quintessential Onion article for reference). And so, as the saying goes, “Don’t quit your day job.” Your life depends on it–though, ironically, it signals your creative death.