My mother came back from a market which bags the products in paper-bags with handles, and asked me to move the bags from the trunk of the car to the house. Being the lazy human I am, I hung a few bags on each arm so I could cut the number of trips back and forth. As I was walking to the front door, the handles of a bag tore, the bag plummeting to the concrete ground. A glass jar of peppers had been smashed in to a zillion little pieces. As you might expect, my mother was furious. "You're so lazy! If you hadn't hung so many on your arm, the peppers and their jar would still be intact!"
I disagree, here's why...
Note that Bag A will have $N_A$ on it regardless of Bag B's existence. Sure, my arm had $N_A + N_B$ ($> N_A$), but it wasn't the thing that broke. So, I conclude, that the tearing of the bag was inevitable, and that the peppers' fates were written by someone other than me (e.g.: manufacturer didn't put enough glue to handle expected weight, cashier put more weight than permitted, etc).
Is my reasoning correct? Or am I missing something that proves that I'm guilty?