Not always true. Sometimes you major in what you love, graduate, get a job doing cool stuff, (get fucked over by an asshole boss, change companies, kinda hate working there every day, find out through the grapevine the asshole fomer boss had been fired for being an asshole, return to the company you liked working at), well paid the whole time, and continue to love what you do so much you don't get enough of it at work and do it more every evening and weekend as a hobby.
But then, my experience is a) a bit dated (I graduated college before 2010) and b) most likely atypical.