I think if I pursued a job in something I really enjoyed, like Art, I'd end up getting sick of it, because of the pressure of the job. And because of how scrambled I'd gotten at just taking it at GCSE.
I wouldn't be as free with it as I would if it were just a hobby.
(Also, in a programme, there was this really sweet line about doing the thing you love best as a second job, because that's where you can really enjoy it.)