What I enjoy painting is ... well, whatever happens to take my fancy. When people like what I do, enough to want to buy a painting, there is nothing better.
The trouble starts when someone says "I like what you've done ... but what I would really like is for you to paint xxx for me." Often this involves the prospective client giving me one or several pictures.
I guess I could refuse ... but I like to please and, remember, most of what I receive for my paintings goes to a charity in aid of eradicating diabetes. So, I want that money!
The first problem is that I'm unlikely to have any emotional connection to the scene/portrait or whatever that I am being asked to paint. I have an immediate fear that the result may be a bit "cold". Secondly, as soon as I start I'm already thinking ... what will please this specific client. I begin thinking "what did he/she say they liked about my other work?", "what colours did they mention?" By comparison, if I had decided to paint that same scene for myself, not as a commission, I would be thinking: "What attracted me to this picture/scene? What does it make me feel? How might I capture that in paint ... thick or thin, hot or cold?" and so on.
So, by the time I get to the point of handing over this long-awaited masterpiece, my nerves are jangling.
Still, experience tells me that most clients seem happy with the result they get ... and the jangling of nerves turns into the rustle of notes to bring a cure for diabetes one step closer. Maybe I don't hate commissions quite as much as I first thought!