Explaining the Obvious as Communication

Reminder: explain the obvious to make sure you and your audience on the same page. Make it not just knowledge, but common knowledge.

E.g. when teaching math, you should always start by teaching math they already know. The point of learning is the interface between known and unknown, and you're not going to be able to guess the exact point. Hence, don't guess, go looking. Start at something they definitely know and then edge up until you hit the part they don't. Bonus: asking them [questions they know the right answer to] boosts their confidence. They shouldn't need confidence, but generally math students are children, and children are weak, so they do need it.

E.g. what is mansplaining? It is often perfectly healthy. Maybe you know and I know, but I don't necessary know that you know. The only way to find out is either to name the thing or describe it. Most small ideas don't have names. Describing an idea is to explain it.

Secondarily, it's entirely possible that you guessed wrong and you're not explaining the obvious. Don't assume, go check. 

When documentation is bad, normally they flip between explaining the obvious and explaining without explanation. This is due to guessing where the unknowns interface is. Don't guess, explain such that you necessarily pass directly through the interface at some point.