... Inverted logic. But you're not alone; several people upvoted your post, so it must be an easy mistake to make.

This :) When brain function less (like sleep deprivation), pattern recognition takes place instead of logic processing ... and  $foo = bar($foo) || $foo; is so close to  $foo = $foo || bar($foo); the association to  $foo ||= bar( $foo ); happens, and tired brain fail to realize they're different

human brains, what can I tell you :)

hmm, its more like logic processing doesn't check pattern recognition ... argument validation, even for brains