Have you heard of lock bumping? I had not until just today. My company sent us a video of the process by which thieves can cut a key and using a simple tap, open 90% of the locks that secure our homes. You can even find a video of how to make a bump key at Wikepedia and a link to buy bump keys!
I guess we use locks only to fool ourselves into thinking we are secure. Determined thieves seem to be one step ahead of the naive public.