Game design is simple, actually

"There are a lot of things people call "fun." But most of them are not useful for getting better at making games, which is usually why people read articles like this. The fun of a bit of confetti exploding in front of you, and the fun of excruciating pain and risk to life and limb as you free climb a cliff are just not usefully paired together."

"In Theory of Fun I basically asserted that the useful bit for game designers was "mastery of problems." That means that free climbing a cliff is in bounds even though it is terrifying and painful. Which given what we already said, means that you may or may not find the activity fun at the time! Fun often shows up after an activity."

"Anything that is not about a form of problem-solving is not going to be core to game systems design. That doesn't mean it's not useful to game experience design, or not useful in general. Also, in case it isn't obvious - you can make interactive entertainment that is not meant to be about fun. You can also just find stuff in the world and turn it into a game!"

Fun in games arises from players solving problems and making progress in prediction, often experienced as mastery rather than immediate pleasure. Designers should focus on posing solvable, engaging problems that encourage learning, skill development, and post-activity satisfaction. Many activities produce transient enjoyment but lack the problem structure that sustains long-term engagement. Interactive entertainment can purposefully avoid fun, serve as training, or transform real-world tasks into games. Game systems design centers on core problem-solving mechanics, while other elements contribute to experience design. Confetti-like effects alone cannot carry a game; meaningful progress and prediction refinement generate durable player engagement.

Read at Raph Koster