Another way that I like to twist the knife is that once someone's injured or sick, their judgment tends to be affected. You can get a lot of mileage out of starting with someone who's highly competent, and then have them make progressively worse decisions as they lose more blood/get more feverish/etc. If you're planning to have someone be rescued in the nick of time, it's a good way to have them hit bottom very quickly.

This is in the beginning of Stranger, when Ross starts out having lost most of his equipment and is out of water, in the desert, with someone chasing him, but feels pretty confident as he's dealt with that sort of situation before. Three pages later, he's been shot and had to cut his arm open, and from there on it's all downhill: he can't figure out which cactus has water, he fails to spot the town, he stumbles around in direct sunlight and gets sunstroke, and finally ends up walking straight into a vampire tree.