Common sayings that cause some confusion, at least to a kid.
A stitch in time save nine.
Saves nine what? Well, saves needing to make nine stitches instead of one. What it really means: A problem should be fixed early, before it becomes a bigger problem.
You can't have your cake and eat it too.
But if you aren't going to eat it, what is the point in having the cake? But it's just poorly worded. More clearly, it means, "You can't eat your cake and still have it." You can eat the cake, or you can have an uneaten cake, but you cannot have both -- at least not with the same cake.
All the King's horses and all the King's men couldn't put Humpty-Dumpty back to together again.
How would the horses put anyone together? But that's not the point. The King's horses and men show that the King has wealth and power. But wealth and power cannot restore life.
Waste not, want not.
So, if I don't waste it, I'll never want it? With modern usage of "want" tending to be simple desire, it suggests that the way to not desire something is to use it carelessly. The real meaning is different, using "want" to mean actual need. And that way, it means that if you conserve something, you won't run out of it, at least not so fast.
What you don't know can't hurt you.
So, all those warning signs are the problem, for trying to get me to know something is dangerous? Not quite. It's more like, "You can't get in trouble for telling a secret if you don't know what it is."
There are probably others that I've missed, or have confused other folks when they were young.