I agree with that. And like most rule of thumbs, it's very useful to go beyond the prescriptive part and ask yourself "why". And as qsort described, doing "one

I agree with that. And like most rule of thumbs, it's very useful to go beyond the prescriptive part and ask yourself "why". And as qsort described, doing "one thing well" enables you to have desirable traits (easy testability, low cost refactoring, etc.).