Other people’s procedural knowledge gaps

There’s been a recent heavily upvoted and profusely commented post about things people want to learn. It’s close to having so many comments in a single day that it should probably have a part 2.

However, the subject seems to inspire thoughts about what *other* people ought to know, and while that’s got a good bit of overlap, it’s emotionally rather different.

So, what do you think other people ought to know? Any theories about why they haven’t learned it already? Any experience with getting someone else to learn something when it started out as your project rather than theirs, especially if the other person was an adult?