Resistance and Opposition
Of course NPCs fight back, but even inanimate objects can present obstacles. A simple, well-oiled lock has low EL; a complex or rusted mechanism is harder. Everything pushes back - when you try something hard, roll your EL against the task's EL.
If you roll a successful 7 and the task rolls a 4, you get effect 3. It's the same fighting a goblin, picking a lock, or sweet-talking a guard, with one very important difference: some things just resist, but others hit back. (You can roll over EL and fail outright; we'll explain soon.)
Resistance is passive. It never uses your turn, but also doesn't generate effect. If a locked door isn't trapped it's not likely to hurt you, though it still has a job to do. When Resistance wins a roll all effect is canceled out; this is the same whether something is resisting the actions of your character, or your character is the one resisting. Locks don't open, rocks won't budge, or poison just doesn't work. It might be boring or frustrating, but it's simple.
Opposition means whatever you are trying to affect is trying to affect you back and it's a contest. The difference becomes the winner's effect. Sometimes the door is trapped. If your opposition rolls higher, they get effect against you!
This absolutely means that on "your turn" the goblin can hurt you, but the important distinction is that Resistance doesn't use a turn - it's virtually always a free action. If the goblin hits you on your turn it's because they spent their turn opposing you, and it takes skill and planning to get another turn. (You can get multiple turns if you're good enough - that's called Splitting, we'll get to that in a bit.)