In another thread someone quoted the saying "you don't fight fire with fire" in a dicussion about what's the best way to act in certain situations. And after a while it occurred to me that, while that might be good advice when it comes to how we act in those situations, it's not necessarily good advice when it comes to dealing with actual fires, for example forest fires.

And that set me thinking about other times we use metaphors which don't actually reflect reality. For example "you can't turn back the clock" - which of course is absolute nonsense. Didn't we all hav to do precisely that a couple of weeks ago?

That's one way metaphors can be treacherous, when they don't actually reflect reality. And the other way is when they might be accurate enough, but they shouldn't in fact be seen as carrying any weight in the arguments where they get deployed.   

For example it's quite true that oil and water don't mix - but that doesn't mean that different types of people don't mix, and yet it gets trotted out in that kind of argument.

So does anybody feel like coming up with a few more examples?