You don't have to fit anything in your head. I often find myself consulting the index at `man systemd.directives` to remember things: https://www.freedesktop.org/software/systemd/man/systemd.dir...

In lot of cases I've found systemd units much to actually be simpler and easier to maintain due to everything being in a simple declarative format. The old alternative is to have a lot of shell scripts that can get very complex, and to consult another few hundred man pages for various shell utilities...