Significance of fasting on the feast of the Elevation of the Holy Cross

Maybe my question is too basic, or isn\'t clear. It\'s just that when I think about it, the feast of the Elevation is a celebration of two very important events, and so it\'s counterintuitive to me that we fast on that day. Someone suggested that the cross itself is a reminder of the cross we have to carry and the things we need to do to be saved, which includes prayer and fasting, but I can\'t help but think there\'s another reason.