Presumably there are four types of persons in the world. To wit:
Those who believe there are four types;
Those who believe there are fewer than four types;
Those who believe there are more than four types;
Those who think the whole idea is cobblers;
Those who don't care (like me).
* Note for pedants.
The list has five elements. This is known as a "joke". I have left you some grammar errors as well to give you something useless to do.
** Note for mathematicians.
We could usefully consider the fifth element as a description of the null set in this context. Feel free to discuss whether the presence of a null set invalidates the claim that dividing a set into four subsets covers all parts of the original set.
Seriously. Really. Strikes me as unlikely that we fit into five professional "categories": Captain Fantastic, the Solo Flyer, Version 1.0, the One-Trick Pony, and the Whirling Dervish (I like the names though). Is there here something really new? Nah, Cast nicked the idea off Hippocrates. This has been around since ancient times when the four types were choleric, melancholic, phlegmatic and sanguine. Truly there is nothing new under the sun. Speaking for myself I was never one to believe we could be pigeonholed. Aye right, “there is no one-size-fits-all solution" - but four (or five according to Cast) sizes? Yep, that just about covers the entire human population.
If you're into self-help books of the Managerial Type, read on.