We sat down to prepare as we are going to teach some theory. That was overwhelming. We understand the theory pretty well, because we use it on a daily basis. However to teach it, we needed to pick a way to present it. That was really exacerbating when you could see millions of ways to approach it... ;_; If you don't make your choice before teaching, then you will not be able to present the material in a coherent way with the millions of parallel universes tearing at you in all directions. (This happens to us quite often in daily conversation. If we block in conversation, then we either have too much to say or have thought of nothing.) Thus we guess that knowing things beyond a certain level may hinder the ability to teach if one is not prepared. Well, we need to go back to preparing instead of rambling here.
Today we overheard people talking about that they couldn't understand this and that. Gradually the spectrum covered all the basic mathematics, by which we mean the lot like calculus, linear algebra etc. OMG. Nowadays it seems very fashionable to declare that one does not understand maths and to take pride in not understanding. People literally form bonds in the not-understand-maths-ship. What is going on? Really, we need to go back to preparing instead of trying to figure out this issue which we accidentally side-tracked into.