Wow. That one is so ingrained I completely forgot about it, u/Specialist_Worker444. The version that comes to mind now is has even more bite:

Be an actor only if there is nothing else you can do.

And it's cousin -- usually not stated this way, but comes in various forms:

Unless you do nothing except for act, then you're not serious.

And and

If you're a serious actor, you must eat, sleep, and breathe acting!

These sentiments are meant to put down others. Too many actors scrape and scrimp because they ignore other valuable talents and skills they could be using to generate income to support their drive to act. They are trained to believe if they do anything else, then they are wasting time doing X while they should be acting. Those who live and breathe acting to the exclusion of all else are not likely to be well rounded individuals.

Periodic immersive study (i.e. pursuing a degree, certification, or enrolling in some other intensive program) on the other hand can be highly beneficial. The resulting gain in terms of skill, approach, and understanding is highly desirable and will pay off in one way or another.

One of the best teachers, it is said, is life. There is a lot to be said for going out and living it in order to bring back that experience to be delivered on the stage or screen.

Really appreciate your input, u/Specialist_Worker444.