Olive Day needs YOU! Love olives? Don't love olives? Come help out at olive day! We will be helping out these fine people at their Childrens tent! Please enjoy the Olive Theory brought to you by How I Met Your Mother: The Olive Theory is based on Lily and Marshall. Ted describes the theory to Robin in the Pilot episode. Marshall hates olives, but Lily loves them, and in Ted's opinion, that's what makes them a great couple; perfect balance.