"A cardinal rule of writing is never interrupt yourself to explain something. If you must bring up an obscure topic, drop informative hints about it as you go along so that you don't end up with the entire explanation all in one place. This keeps you from skidding to a stop and sounding teacherish. Otherwise it's better to omit the obscure topic altogether, or as mothers might put it: if you can't say it interestingly, don't say it at all."