Why would this php not work but would work this way?

[hunterpiggy]

\[code\]if ($sess_uid == $WallID){//}else{Run Action}\[/code\]WorksBut\[code\]if (!$sess_uid == $WallID){Run Action}\[/code\]Wont work. Why is this? I want the code to fire off if both Ids don't match.