There are two subtly different things here, "monads" as a concept and specific monads. If I ask you, what's the thing in common between async functions, nullabl

There are two subtly different things here, "monads" as a concept and specific monads. If I ask you, what's the thing in common between async functions, nullable types, exception handling, sequenced evaluation, and arrays, and you only know, say, Java, Scheme, and Python - you'll probably not see anything. Nonetheless, these are all monads, and learning specific monads helps in lots of other languages. Optionals are nice in Java. Arrays in Lisps. Error handling in Scala. But the "universality" of monads escapes these languages. I would kill for better monadic error handling in Go, but conversely I would have little use for monadic I/O or futures. The critical mental step is seeing the commonality in all of these, which is really only possible in languages at that level of type sophistication. And necessary in Haskell where the particular combination of purity, laziness, and HKTs means monads are the only way decent way to do most of these. Once you see that commonality you can develop tools - patterns of mental reasoning about code and idioms for writing code - you can also use when dealing with the specific monads or nearly-monads in other languages. But you can't show that property in examples in a single other languages, and it's difficult to show how some deep structure is shared in examples spanning five languages.