As an aside, I've had to treat my players over the past year or so with some hard-won lessons about being prepared, because our play style used to be a lot more lax on that, and after being exposed to some of the excellent DM's here, I'd wanted to introduce that element.
Alas, simply saying, "you will occasionally run into things tougher than you, don't be afraid to run" is not the same as actually throwing the situation in. I've had PC's pay with their lives before when they "meta-gamed" the idea that I wouldn't put something in too tough.
One squad of Bone Devils, 1 Umber Hulk, 1 group of assassins, and 13 Hill giants later, they now don't enter unnecessary combats, and they are careful to be wary of traps that could overwhelm them.
I once had them stumble across a group of hill giants living in the mountains under care of a cloud giant. In the old days, they would have tried to charge in. These days, they watched a tribe of orcs get smashed to pieces by boulders, and did the smart thing: They offered to trade with the giants.
Got some good deals, too, and they know where to go when spring trading resumes.
