bbatsov/ruby-style-guide — pull request #325 by cheerfulstoic (2014-06-25 03:45:25+00:00)
Title: Using unless for all cases of 'if not' isn't natual to an English speaker

It is much better to use either if not or unless depending on if the condition is exceptional.

I feel like following this rule (while it make take some getting used to), leads to generally more readable code and more thoughtful coding