I find documentation to be relatively straightforward to write. The issue for me is sitting down and slogging through the activity, which seems almost antithetical to writing code. It's like doubling the work in a far less rewarding way. And then you have to go back and update it any time the code changes. It's a sort of necessary evil I suppose...I think most of the problem is that devs just can't be fucked to take the time, and I'm often guilty.