Sharpie Sandbox captures it perfectly here. Just because you explain something to someone doesn’t mean they’ll understand it. This is partly because they hear exactly what you say, not what you mean.

Precise word choice matters when you’re explaining new concepts (like subtraction). It’s quite easy to see how someone could misinterpret “take one away” — isn’t it?

from Sharpie Sandbox:

“If you say: here are two different numbers, now take one of them away. I’ll say: easiest math ever! …And then fail three years in a row.”