Specialisation is for insects
“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 Heinlein, Time Enough for Love
Be wary of becoming a specialist, whether it's in your career or in your personal life. Certainly expert knowledge and being highly skilled are good things, but being a specialist has its downsides too.
The Curse of Knowledge
One big problem from becoming a specialist is that it, ironically, can make it harder for you to find innovative solutions and share the knowledge that you've spent so much time specialising in. The more you know, the harder it is to approach the problem with a fresh perspective. The more likely you are to accept certain starting assumptions as necessarily true.
Thinking laterally and 'outside the box' requires that you are able to take ideas and theories from one setting and combine them in a new way in another setting. As Charles Duhigg points out in Smarter, Faster, Better, "if you consider some of the biggest intellectual innovations of the past half century, you can see you this dynamic at work. The field of behavioural economics … emerged in the mid 1970s and 80s when economists began applying long held principles from psychology to economics, and asking questions like why perfectly sensible people bought lottery tickets."
Perhaps this problem for specialists is also related to the findings of Professor Philip Tetlock, author of Superforecasting, whose research has revealed that specialists are bad at making predictions about the future. As he puts it, "The fox knows many things; the hedgehog one great thing."
Tetlock found that foxes tend to make better, more accurate predictions about the future because they are more able to see the bigger picture and apply many different lenses to the same set of facts. But what's even worse is that specialists also tend to be far more confident in their opinion or prediction, even though they make worse predictions than knowledgable non-specialists!
Of course, this isn't an argument for ignorance or refusing to go deep on a topic. It's an argument for keeping in mind breadth as well as depth. As the quote at the top of the page suggests, insects may be highly specialised to their specific place in nature, but you are not an insect. Nature has a nasty habit of testing the limits of living things, and the theory of evolution tells us that only those who can adapt will survive. When you're hit with an unknown unknown, it will benefit you to be a fox and not a hedgehog.