Functions in the lambda calculus are always unary - they only take one argument. Functional programming is based on the lambda calculus, and it is useful to learn to appreciate unary functions. One useful way to train your brain to think functionally is, when you find yourself writing an n-ary function, to stop and consider how to rewrite it to be unary. Soon you will find that you have many small, composable functions that are much more portable than the ones you are used to writing.