[sanitycheck]

I'll agree with all this, particularly the first paragraph.

I've burned out a couple of times and the fix has been to stop for a while and do other things. After a few months I catch myself coming up with ideas for projects, writing code, etc - that's when it's time to go back to paid work. Obviously that's more disruptive to perm employees than to me as a contractor, but I hear rumours that such things as sabbaticals and sick leave exist.

Becoming an "expert in X" seems to be easier than it might initially appear, it's sometimes the path of least resistance to fall into a specific niche that may or may not exist a few years later - but while it does you are in demand. (I don't unreservedly recommend it!)