Thomas Shey
Legend
Absolutely the PCs should sometimes find themselves in fights they didn't see coming. Ambushes, blown perception rolls, or just simply getting caught off guard.
The question revolves around those fights the PCs can see coming and thus can - if they want - avoid or mitigate.
My only point is that if you're not getting a lot of character turnover, one way or another, as a GM, you're setting things up so that happens; it won't happen just as a consequence of how the players are operating without GM enabling. (The exception, again, is in no- or very low combat games--and I do mean very low).. People can have ongoing characters in a game with significant combat only if they have some kind of an edge, and the edge can't come just from them; the GM has to make it available whether its in-game or out-of-game.