Customer: *hands me two identical coupons*

Me: “You want to use two 20% off coupons? That takes two dollars off each item. Using a five dollar off one would save you an extra dollar. Would you rather use that one?”

Customer: “But using these two coupons saves me more.”

Me: “Actually, you only save four dollars by using those. The five dollar one would save you more.”

Customer: “But using more coupons saves more money!”

Me: “That one coupon is worth more savings than those two, though. That coupon would save you a dollar more, and you can use those two 20% ones another day. Five dollars is more than four dollars.”

Customer: “No, it’s not! I don’t understand how you think that!”