Why is it humanly impossible to eat just one doughnut?

For years, i have been a consumer of many, many doughnuts. cake, jelly-filled or just plain. it makes no difference. the problem is the number. I can never consume just one doughnut. am i alone in my “doughnut caper”? it must be the devil saying to me, “john, just one more doughnut wil not make a difference, go for it”. i know its not greed, since my wife hates doughnuts, there is no competition here. so, what is it that makes my hand reach for a second and a third and a fourth doughnut?