Twenty years, twenty lessons

Mark Rosewater is a game designer for Magic the Gathering, an immensely popular trading card game. He gave an hour-long talk at a game development conference about the lessons he learned in 20 years of game design. Afterwards, these lessons were published as a three part column.
What I've learned over the years is that you shouldn't change your players to match your game; you should change your game to match your players. Don't get yourself into a fight you're probably not going to win. Human behavior is a powerful force. We are creatures of habit and instinctually fear change.
The articles focus on game design, but the lessons are applicable to anything that requires design thinking.

Mark precedes every lesson with an anecdote, explaining what went well or what didn't. Another one of my favorites:
Players' need for individuality is strong, which means that they will be looking to find a small corner of your game where they can feel a special connection. Big things tend to gather too much attention, so it's in the smaller details where players will attach the strongest emotionally, which means that the details are actually far from insignificant.
I don't have any prior knowledge of the game myself, so don't worry about not understanding parts in spite of the topic. If the first six lessons piqued your interest, here are parts two and three.