Don't Give Up Your Day Job Meaning

(idiomatic, often humorous) Somewhat sarcastic but usually good-natured advice used to criticise a person's degree of talent (especially in music or other performing arts), implying that he or she could not make a living from it.

Example: 2006 July 3, Viv Bernstein, "Said Makes His Case for Success in Nascar," New York Times (retrieved 11 Oct 2015):
  "I remember after the school was over," he said, "I went up to the instructor just completely wound up like: ‘O.K. man, how do I do this and become a real racecar driver? I want to quit my job and do this.’ . . . And he goes: ‘Other Sports Beckon. You suck. Don't give up your day job.’ "