Past Commercial Success.
Those ideas are called "tropes" or clichés; you can google for those; many TV tropes used.
Steinbeck may have been the original author of that particular big-dumb, little-smart duo; I'm not sure.
The real source is other authors that do something original that resonates, or succeeds with great commercial success. You can often find these in past best-selling fiction, or movies.
For example, I think a modern trope in the making is this idea of a young teenage vampire falling in love with a non-evil teenage girl. Similar to Buffy the Vampire Slayer (Buffy is in love with a vampire she should kill); and of course Twilight, but I believe it was in print a decade before those came out. But the idea seems pretty recent to me; I don't recall this theme anywhere during my own teenage years.
In a deeper sense, we have stereotypes.
Our psychology prefers the Plus Column and Minus Column be roughly balanced.
Lots of Muscles = Lack of Intelligence. The big dumb gym rat.
Physical Prowess = Lack of Intelligence. The admired school quarterback.
Lots of Beauty = Lack of Intelligence. The clueless beauty contestant.
Sexually Attractive Men = Shallow narcissists, love-em-and-leave-em jerks.
Lots of Brains = Lack of muscles. The nerd in school, getting bullied.
Lots of Brains = Lack of social skills, or (paradoxically IMO) an inability to communicate effectively with others.
Rich = lack of empathy, a sense of entitlement.
Our culture is filled with these stereotypes, for nearly every positive feature we search for a negative to balance it. Then authors can pick some that cause a natural conflict; Steinbeck took two and made them work together: The physically weaker intellectual taking care of a much stronger mentally disabled man.
A modern take on "Of Mice and Men" would be a professional in a high-intelligence mind-focused field (science, medical research, etc) that, out of love and duty, takes care of a big, strong autistic sibling after the death of their parents. That might have commercial success, considering the explosive epidemic of autism is leading many parents to worry about how their own autistic children will be taken care of after they pass away, or age to the point they are also disabled.
As a writer, becoming familiar with stereotypes, clichés and tropes and balancing character traits can be very beneficial. Of course these are built into our psychology, so many writers do it naturally, but some familiarity lets us both use stereotypes and break them. Sherlock Holmes is a genius, but but breaks the stereotype in one way: He can fight. He sticks to the "genius" stereotype of being socially awkward, in fact that tends to be highly exaggerated in all the modern portrayals of Sherlockian Detectives.
In order to predict the kinds of characters in a story (or for a writer, decide the kinds of characters in a story), look for the balancing traits. If a guy or girl is dumb, look for a counterpart that is smart. If they are rich and egotistical, a sidekick or love interest that is not.
In comedy, we often see wrong matches: Dumb and Dumber. Cheech and Chong. In the Big Bang theory, we begin with a bunch of nerds with all the same traits; no balance, and the most extremely unbalanced (Sheldon) is both the smartest and most socially disabled, the stereotype amped to the max. But it also begins with them presented with their opposite stereotype; Penny: beautiful, promiscuous and dumb blond.
Obviously you can still find commercial success with worn out stereotypes. Personally I avoid them, but I do consciously look for balance in my characters, and for a team a complementary mix of traits. I try to stay away from the most common stereotypes (I don't mind a smart jock, I can some other balancing deficit for her).
But anybody interested in writing (either analysis or execution) should be looking for the tally of pluses and minuses in commercially successful fictional characters (and teams) to see how its done. And realize that the balance of strengths and weaknesses (in heroes at least) is something to be achieved, not overcome. Evil typically comes with a built in flaw: It is evil! So adding more flaws is not as necessary. But you still want balance! The stronger you make the villain (smarter, more skilled, more attractive, more socially adept), the more you must stress their flaw; if evil is their only flaw then you must go to ludicrous speed on the evil. This can produce a trap for the writer: Precluding the ways the hero can plausibly defeat the villain. So the ending must be kept in mind; not necessarily planned, but while writing, a good notion of how the hero can prevail against a super powerful villain, what weakness can be exploited to win.