Agreed. This is just like when I tried to grok monads. So many articles trying to tell me how simple they are... yet still so many articles needed to explain it (and I'm none the wiser)
pure :: a -> List a
flatten :: List (List a) -> List a
map :: (a -> b) -> List a -> List b
For lists, the implementation is as follows:
pure x = [x]
flatten [] = []
flatten (x:xs) = x ++ flatten xs
map f [] = []
map f (x:xs) = f x : map f xs
flatMap f m = flatten (map f m)
m >>= f = flatMap f m