I used to live with a guy who was the same with chocolate biscuits. Once, I bought a packet of chocolate "Hob nobs" (very nice), eat one and went out. When I returned, the packet was full and unopened. "So what's the story" I asked, and it turned out that this guy had had one biscuit from the packet, then another, then scoffed the lot. So he went out and bought a new packet (sweetie) and took one biscuit out so I'd be none the wiser. Then the same happened and he scoffed the whole packet. Then he bought another packet and left it sealed for fear of doing the same: "I can't eat 3 packets of Hob-nobs in a day"