I had to unlearn a pattern of thinking that put conditionals first. Code like

  if ( $DEBUG ) {
      print "debug info\n";
  }
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use to fly off of my fingertips without much thought. It took a while to try writing   print "debug info\n" if $DEBUG; Once I saw that this could lead to less cluttered, easier-to-read code, the change was easy. Using "unless" took a while longer, since I balked at the built-in negation. I use it sparingly, for things like   unlink $file or die "$file: $!" unless $DEBUG;