I think this is really a corrupt idea that floats around, and many times influences younger people away from trying to find a career and instead landing themselves in crappy jobs.
For example, some people like to work on cars, but they don't get a job in that because their dumb uncle said this to them, so they spend their time grinding away at a fast food joint and going nowhere in life. Maybe they can poke at their 15 year old car once in a while, but overall their quality of life is not very good, and they basically never get to work on cars. If they had instead gone into professional car service, they would have a decent paying job and be able to reach a comparatively higher standard.
Does that mean that it's not work? Of course not. You will always have to do work and it's not always pleasant, but at least you can leverage your interests and strengths. If you get bored or annoyed at working on something you used to think was fun, then take a vacation or find something else do to over the weekends to get your mind off it. If you are annoyed that it's not fun anymore, then -- welcome to adulthood.
That is truly the difference between having a job and setting yourself up for a successful career.
To give an example, two of my passions can be said to be writing code and playing music. Of the later passion, it is really difficult to make a career out of it that is anywhere comparable to any coding job, and (knowing what it's like in a local band) it's actually more work than a coding job in most cases; the best bands execute a lot on the sales / marketing / promotion side in any case, a side that I'm personally weak at. So music has becomes the "hobby passion", while the "code passion" pays the bills.
(Granted, in some cases it is actually possible to combine the two and do even better. DSP engineers for instance are in pretty high demand as far as I know.)
For example, if you have a passion for say writing and computer science, I would recommend to get a job in CS, since money/time ratio is usually higher there.
Or perhaps the size of the hit varies - for some people / passions it's small or zero, for others it's big, with the peak of the curve being "some but not too much"?
I drew another consequence and quit the field instead and in turn rescued my passion from fizzling out. And while I'm only passingly interested in what I'm doing now, for me, it was worth taking my hobby back.
It's not an entirely hollow phrase, but something to consider at least and maybe one should ask themselves if they're ready to be passionate about something for 8+ hours a day.
I think the dumb uncle is correct. Although, if you like something well enough, then you usually become good at it, which in some cases means that someone will pay you for it.
It's up to you if you want to extract the fun and convert it into cash. It may be worth it, or it may be not.
I have a lot of friends in the audio field, and something I've noticed is that doing your passion for a living can take the fun out of it.
For instance, my friends in the audio world don't sit around listening to new loudspeakers, or designing new loudspeakers. They mostly spend their time marketing products and filling orders. Working in audio isn't a whole lot different than working in any other retail field.
But when I work on audio projects? I can do whatever I please, because I'm not doing it to pay my mortgage.