All the fucking time in, say, any FPS Campaign where you can be 1-shotted, EVEN IF there's only one possible occurrence that may happen.
You can take Flashpoint; Dragon Rising for instance. In that game, you can, by any weapon, at any distance, at any time, be 1 shotted as a bullet flies through the air and hits you on the head. Otherwise, they just miss you 80% of the time. The other 20% it's either your head, and/or your limbs.
So, you run, run, run some more, run, shoot some asshole, repeat. Than, after 25 min, and you're almost seeing the end of the chapter, you're insta-killed. By a simple shot.
... Than you've got to re-do the whole thing all over again.