This is why I try to work as little as possible. I either hate it from the get go, or it slowly transforms something I enjoy into something I resent.
I've been working in software for 20 years, and even though I was quite passionate about it in the first 10/15 years, my interest has declined steeply for the past 5... Since I'm only turning 40 in a couple weeks, sometimes I dread what the future will be, since I still got another 28 years to go (at least - retirement minimum age keeps increasing). I'm not even halfway and I'm already losing my spark, I can't possibly imagine how fed up I will be in 10 or 20 years.