the world exists independently of the players
This is a huge piece of the puzzle that prevents people from grokking this style of play.
The world exists independently of the players
and their characters.
This is also one big reason why neutral referees use random tables and random rolls, to remove even the potential of their thumb being on the scale. You design your charts and table independently of the players and characters. When the PCs interact with a space, you roll on that table, whatever comes up, comes up. You don't stack the tables for or against the PCs. You make them as neutral as possible. As honest to that part of the world as possible. If you're in the mountains, things that live in the mountains go on the wandering monster chart...regardless of what HD or level the monsters are and regardless of what level the PCs are.
For example, the PCs are on their last legs, down all spells, have few hit points, and are trying to rest to recover...but they got into an argument and start screaming. So the referee rolls a wandering monster check, yep something's out there. Roll again, it's orcs. Roll again for number appearing...ouch. The referee rolls 117 orcs...so that's what there are. The referee rolls on the reaction table, they're immediately hostile...so that's what they do. That's what they're dealing with now. Not because the referee decided to, but because the referee is neutrally following the procedures of the game.
If the GM
decided there was a warband of 117 orcs over the next ridge
because the PCs start screaming and shouting at each other, then
decided that warband
will hear and
will come to attack, most people would agree that's terrible GMing. The opposite of that is the GM who decides that no matter what the PCs deserve a break and will refuse to roll for wandering monsters. Padding and softening the adventure to suit the PCs and their current state, most people seem to think that's good GMing...but I disagree.
It's a game, you play to find out what happens. You don't decide before hand what's supposed to happen...good or bad.