[lmm]

I think what you're describing is a case where you can't understand what those helpers do, and therefore can't understand what the function that calls them does. I maintain that if each individual function makes sense then the whole will too.

[pshc]

This holds if the small functions are built around a coherent top-down design, respecting each other's invariants. Once the project is too large to fit in one's head, it is no longer sufficient for each function to be 'correct' in a local sense.

[mannykannot]

Sensible, understandable functions can be assembled into complicated, incomprehensible programs in exactly the same way that the sensible, understandable operators of a programming language can.