Name a place you go where you give something to someone and then pay them to take it.  Only one place comes to mind, and it's the Post Office.

Think about it.  Normally, you go into a store and find something you want to buy.  You go to the cashier, hand over some money, and the cashier lets you take the item with you.  But the Post Office is different.  Not only do you give them an item, but you also have to pay them for it! 

Of course the transaction makes sense, but every time I leave the Post Office I feel like I've left something behind.  When I come and go from a store like Walmart, I subconsciously understand that there has been a balanced transaction.  "I have less money in my pocket, but I get to carry this plastic bag instead."  The plusses and minuses cancel each other out, and there is equilibrium in the marketplace.  At the Post Office I experience a double negative and can't help but get the feeling that I've forgotten something.

The next time I go to the Post Office, I'm going to ask for a plastic bag to carry out.  I know I'll get a curious stare, but at least my subconscious will understand that I've had a fair transaction.  "I gave them money, and they gave me this bag."  And there will continue to be balance in the universe.