And often they’re really good at the one thing because they have their hands in many things.
Cultivating a breadth of knowledge often isn’t just being mediocre in a bunch of subjects, but about broadening one’s awareness to potential connections and opportunities.
If you can’t go deep on anything, that shallow knowledge may not get you very far.
But if you can go deep on X subject with enough surface level knowledge of a variety of potentially related topics, you’ll be able to accomplish far more interesting things than someone with equivalent but exclusive knowledge of X.
My bosses task me with being the 'dot connector' for a bunch of specialists. Seems to work out well.
If you really want to know a subject well beyond theater, you obviously would have to know many adjacent subjects and many seemingly unrelated subjects since "subjects" in this context are just imaginary divisions within human knowledge.
If your interest is credentialism though then the unrelated subjects are just a complete waste of time and most likely the adjacent subjects are just a distraction from memorizing your lines for the theatrical "subject matter expert" performance.
It is really a question of the best way to pretend to be a great mind when you are average and that is to specialize to a degree that minimizes the amount of people who know what you are talking about on the subject of interest.
We have built an entire class of society on this method.
“A human being should be able to change a diaper, plan an invasion, butcher a hog, conn a ship, design a building, write a sonnet, balance accounts, build a wall, set a bone, comfort the dying, take orders, give orders, cooperate, act alone, solve equations, analyze a new problem, pitch manure, program a computer, cook a tasty meal, fight efficiently, die gallantly. Specialization is for insects.”
― Robert A. Heinlein
You can't be a generalist without being an expert.
For each polymath there's also Michael Jordan and golfing.
Although thinking about it a bit more right now, I don't see why someone shouldn't be able to be great at a wide range of physical activities to be considered a polymath - as opposed to both physical and mental activities, or solely just intellectual activities
If someone excels in a great deal of, say, a number of sports (which I admit, would be nigh impossible in the current age with all the professional sports leagues and their exclusiveness), one could probably argue that that person is a genius