I had a bike stolen years ago. I actually did lock it up (with a U-lock) but I locked it up outside and that was foolish. You see, first the thief came by and stole my unsecured bike seat. I should've brought the bike inside, but no—I assumed what had been told to me, which was that a U lock was "indestructible".
Well, I found out the hard way that that style of lock was very much destructible. The bike theiving SOB came back and managed to break the U lock, which I found laying in two mangled parts around the base of the pole where my bike had been locked up to.
I do worry about how easy these locks are to get open. I watched a tone of videos on youtube about how to pick locks too. Some people make it look so easy. I'm definitely going to keep my bike inside from now on.
Supposedly some bike thieves even use nitroglycerin to freeze the locks and then just crack'em...
Really? That's worrying. and a little bit cool as well XD