Work etiquette

For the life of me I will never understand why some people act the way they do here. Case in point....I left my locker unlocked yesterday by accident. Come in this morning and someone had gone in there..TORE the box open and stole 5 of my 11 granola bars I keep for breakfast. I eat light in the morning for various reasons. But this really ticked me off because the person did it once before...why I bought the lock. Other employees choose to either keep a lock or not. I chose to after I had a thief take my things.

One other time an idiot, not on my floor, stole the lunch of a pregnant lady...and yet another time someone's drink, later...all the cheese from this person's lunch...we even have a sign in the breakroom stating that whoever is stealing from the breakroom needs to stop.

What in the world possesses a person to behave in such a trashy manner??????????