This is the problem: I don't really know. It doesn't help that POSIX sh (and GNU Bash) are objectively terrible programming languages, and that it takes a decent amount of masochism to "enjoy" them in the way that (I think) engenders competence.

For me, it was a lot of scripting and then iterating on those scripts when I realized that they conceptually broke down in places (even if they never broke in practice). Things like spaces where you don't want them, needing to pass around data that might be too large for `argv` (because of stack limits), etc.