Having a discussion with a friend about our views of GMing, I realized that we take very different approaches to what our worlds are.
My view is that when I GM, the world exists as-is before the players start playing. What I mean by that is facts of the past can't change based on what my players do.
My friend has what you might call a more player-focused plot. He rewards any sort of intelligent player action by moving the plot along as long as it can be done without seeming like that.
Here's an example. Let's take a game where there's been a murder. And let's say I decide that the person was killed by a lot of sleeping pills being put into their food. But the players, seeing no sign of injury, immediately start testing for well-known poisons.
My approach would be to say that all of the tests come up negative, but of course if any of the tests would suggest the presence of sleeping pills, I'd say so.
My friend would confirm the presence of some poison that they test for.
His way has the advantage of helping the players feel smart and moving the plot along without slowing down the action unnecessarily. But I really prefer my way, because I feel like I'm setting up a puzzle for my players. However I have definitely noticed that this has its issues because the problem of setting up a solvable-but-not-too-simple-puzzle is not exactly trivial. I usually refuse to give any more hints that I wouldn't expect to be present on the scene, and once this even resulted in players basically saying to each other "Well, I don't know what to do."
What's your style? Is it something in between?