This is probably going to come across as arrogant... it's not meant to. Being smart is relative to whom you work with, live with, associate with. It is also relative to your interests. I might be smart about, say, specific kinds of computer software, but not about medical heart replacement valves, small engine repair, or sales techniques. With this caveat, I think the following applies to anyone who is smart about something.
The trouble with being smart is that you sometimes forget what it was like to not know anything and assume that everyone else is also smart in the same way you are.
When you do this (and not everyone else knows what you think they know) people get angry at you because you're talking over them. This leads you to become pedantic and you begin to explain everything, even things that are well known to the people you're explaining them to. This also makes people angry. You learn that you can't talk to most people about your interests and to choose your conversations carefully.
There may be another class of conversational and relationship smarts that I haven't learned about yet...