Costco saves me from my own stupidity

So I'm at Costco today for my regular weekly run. It's just down the hill from me and I use it like a regular supermarket. Today I have with me the coupons they send me monthly, which I've carefully clipped and neatly arranged in the order in which the aisles are when I go around the store in normal counter-clockwise fashion. I have them perfectly arranged in my shirt pocket and as I hit each aisle I make sure to carefully check each coupon to make sure I am buying exactly the right quantity of each item so as to maximize my savings. When each item is in the cart in the correct quantity, I rotate the coupon to the back of the stack and move on.

After I've checked out, I make sure to double check my receipt to make sure I have been given the correct discount, amount and quantity, for each and every item I've bought. As usual, the receipt reflects that the Costco computer system has been flawless, but you never know. Dishwasher tabs, -$3.25 x 2, check. Mayonnaise, -$2.25 x 3, check. Et cetera.

It is not until I get home that I realize: *I have not given them the coupons at the checkout. They have given me the discounts automatically.*

I knew that their system gives you all the coupon discounts for all eligible items in your cart once you scan the first coupon in your stack. I didn't know that the systems is now in "Aw, screw it" mode, where you now just automatically get the discount price with an implied virtual coupon. Nice.