>> full of aspiring actors waiting tables, aspiring writers

I perceived the argument differently. A closer analogy might be that if you want to make it big as a screen writer, you should do something besides writing during the day, so you have the mental energy to write your screenplay at night.

(not arguing the same point myself - if you want to become a great writer, you should be writing all the time. This might make sense if you have already developed your writing skills sufficiently).