I don’t like to use the label “smart” because there are many positive ways of being human, all of which involve using your brain. Here I’ll play with a definition of it anyway:
Smartness is the ability to sort statements by their knowledge value.
A mathematician writes a proof, which is a sequence of statements, each giving an essential piece of knowledge to decide a previously-undecided truth. It isn’t about brevity: the particular writeup may contain many other statements that explain things to the audience. A compentant mathematician would be able to point out which statements are essential to the proof, the statements with the most knowledge value.
As a counterexample, imagine someone uttering, “Education needs to be disrupted.” (I’m not pointing fingers, many of us have.) The issue isn’t about correctness. We have a mutual understanding that the term “needs” is probably too strong. And the statement may be encapsulating many other thoughts about why education needs to be disrupted. But a smart person should recognize that identifying a significant component of education that can be changed within a broader context, or a method of disrupting education that works in the long run, would both have far more knowledge value.
Actually I’ll revise the definition to be more abstract: smartness is the ability to sort objects by some property value. Smart photographers can sort pictures by their emotional value. Smart comedians can sort jokes by their comic value. In an Esquire interivew, Woody Allen says:
I don’t think of the joke and then say it. I say it and then realize what I’ve said. And I laugh at it, because I’m hearing it for the first time myself.
Taken to the extreme, this defintion suggests that creative endeavors are more about perceiving value than producing it. My belief, which I won’t justify here, is that this is true, though production also requires well-practiced techniques. For example a basketball player needs to have well-practiced shooting techniques but also (more “smartly”) needs to be able to perceive the value of taking a shot in the current situation.