At this point we're crossing whether it's a problem with the scenario or a problem with player attitudes. If you're losing a fight, RUN. Perhaps I thought it would be a challenge, but the monster keeps getting high criticals (I'm not using D&D as the example here, obviously), lesson learned: use something less powerful, give it a smaller weapon, something like that. If you stand there fighting a battle you're clearly losing because you assume you'll always win, "Here's your sign". Which is not to say come from behind victories don't happen, they're just hard to pull off.
One of my favorite settings dismisses "balanced encounters" because "real life doesn't work that way".