Things I Wish I Knew When I Started Playing "Developer"

I'm a gamer, and some of my favourite articles to read about computer games are those click-bait posts that read "Ten Things I Wish I Knew When I Started Playing Pac-Man!".
When you're playing computer games, it's easy to miss things that are obvious to others, and these posts can help you to understand a simple game mechanic that you'd otherwise have not used. It got me thinking about the things in my own career that I found out about too late, or didn't fully understand until much later than I needed it.
We'll cover both the technical and the conversational, so join me, as I introduce you to Things I Wish I Knew When I Started Playing "Developer".