That's fine for a hobby; specifically a hobby where you plan to spend 90% of your available time reimplimenting crappy equivalents to things you get on day one

That's fine for a hobby; specifically a hobby where you plan to spend 90% of your available time reimplimenting crappy equivalents to things you get on day one of using an engine. In other words, a hobby project where the point is the exercise and has no need to actually ship. Just pray that you're never employed to be the #2 developer to someone who built their own game without an engine. "Why would there be documentation? Just follow my inner voice."