Rubber duck debugging, in writing
Half the questions I write in a channel never get sent, because I figure out the answer somewhere in the middle of writing them, and I've stopped thinking of that as wasted effort.
z-index: 9999
A size dropdown on a client's product grid kept rendering underneath the row of products below it, and the 9999 already sitting on it had been doing nothing at all for two years.
git bisect
I bisected a broken stylesheet by hand last week, through a pile of backup copies on a live server, and it made a better case for version control than anything I've said out loud.