Comment by codethief

One could also phrase this principle in terms of entropy (in the information-theoretic sense): If I read some code and come across filter() and map(), I already have a pretty good idea of what the code is doing, without even looking at the filter criterion or the mapping function. Entropy is low. (There's only so many filter and map functions you could write for any given type or pair of types.)

Meanwhile, if I see reduce(), "anything" could happen. (Well, of course not anything but the set of possible reducers is surely much larger.) So entropy is high.

Avoid high-entropy constructs in your code. Try to keep entropy as low as possible. (For the same reason, code with a principled approach regarding side effects is a lot better than code where any function could mutate global state at any given time.)