>>> !! 0 false >>> !! "0" true #### >>> not not 0 False >>> not not "0" True #### irb(main):002:0> !! 0 => true irb(main):003:0> !! "0" (irb):3: warning: string literal in condition => true #### DB<102> !! 0 => "" DB<103> !! "0" => ""