That specific key is for a Master warded padlock. This key has been cut down (very roughly) into a pick key. The space left by the cut-away material will now bypas the wards in the locks. However, the active cross at the end is too thin and can easily slip off of the unlocking spring. It will open most of some of the Masters it will go into but not all of them.
Nothing is foolproof to a talented fool. Wisdom is not just in determining how to do something, but also includes determining whether it should be done at all.