The key thing about a game is that a game has a pre-defined goal: capture the flag, defeat the other group of guys, shoot the main boss, whatever.
As such the game has already constrained not what the players *can *do, but what the players *want *to do.
Think of a hypothetical exploration game where the sole purpose is to wander around and see cool sights, fanciful animals, weird plants, etc. That’s it.
In this “game” the game world does not have to be infinite in extent. It just has to be large enough that very few people wander all the way to the edge. We can help achieve that with ever less simulated square mileage by doing things like not starting the player near an edge, putting forbidding terrain near the borders, etc. We are setting up soft limits which tend, not demand, that the user behave in ways the designer wants. Meanwhile the vast majority of users will *not *choose to scale the high overhanging cliff or swim the raging rapids. They’re exercising legitimate free will to explore the easier route despite the fact the obstacles are, unbeknownst to them, placed there deliberately as behavior controls. We can even do subtle things like put more, and more brightly colored, animals in a subtle gradient towards the center of the game space. Folks seeking animals will sensibly turn towards the gradient and unwittingly away from the edge of the world.
Switching gears …
Insane real life humans have truly wild levels of free will. Much more than you or I do. They might be chatting nicely with you on a park bench then suddenly bite your face off while screaming Shakespearean love sonnets. What we call civilized sane behavior is about the “designers” of our collective society limiting absolute free will by imposing soft limits. With the result that sane people don’t think to shout sonnets while face-biting. And non-psycho-criminals don’t think to face-bite, sonnets or no.
Any of us *could *do either or both of those things any time we wanted. But we don’t tend to think of ourselves as being *prevented *from doing that; instead we don’t even think of the possibility.
So ISTM as all this relates to actual game design, the ideal design goal is to present enough of a structured reward system that players are “pulled” towards game paths that you provide for and not pulled towards game paths that aren’t. Yes, you do need some room for sandbox free play. And the less goal-directed your game is, the bigger the sandbox must be. In terms not only of geography and variety, but in terms of actions players can take.
As an example:
I’m also not a gamer. But I bet there’s nothing that formally prevents a World of Warcraft raiding party from surprising a defending force with a hail of weapon fire then promptly sitting down in the open to have a picnic with some beers. The game doesn’t need to prevent that *as such *because the players won’t think to do it. And the defenders, be they other people or be they bots, don’t need a special rule for what to do when encountering picnickers. “Pursue and smite visible enemy” is a good enough rule to appear as intelligent behavior to the foolish picnickers as they’re being killed.
Hope some of this is somehow relevant to the area you’re musing about.