Anytime that, without being invited, being asked, we try to teach somebody else something, anytime we do that, we convey to that person, whether we know it or not, a double message.
The first part of the message is: I am teaching you something important, but you are not smart enough to see how important it is. Unless i teach it to you, you'd probably never bother to find it out.
The second message that uninvited teaching conveys to the person is: what I am teaching you is so difficult that, if I didn't teach it to you, you couldn't learn it.
The problem is that we human being like teaching. We are a teaching animal, as well as a learning animal. We have to restrain that impulse, that habit, that need to explain things to everybody... unless we are asked.