A useful explanation gives you a way to check whether you understood it.

Many explanations stop at the point of sounding reasonable. You nod, it hangs together, and nothing tells you whether the understanding you now have is the right one, so the first real test comes later and costs more. A good explanation hands you something to check against. A prediction, a worked case, a question you should now be able to answer.

After an explanation, ask how you would know if you had it wrong. Try to use it on one small case straight away. If you are doing the explaining, finish by asking the person to apply it rather than asking whether it made sense.