How to get really smart

A customer at the fish market marveled at the owners quick wit and intelligence.
Tell me Jimmy, what makes you so smart.
I wouldnt share my secret with just anyone, Jimmy replies lowering his voice so the other shoppers wouldnt hear, but since your a good and faithful customer, I will let you in on it. Fish heads, eat enough of them and you will be positively brilliant.
You sell them here, the customer asks.
Only $4 a piece, says Jimmy.
The customer buys 3. A week later he is back in the store complaining that the fish heads taste horrible and he isn't any smarter.
You didnt eat enough, says Jimmy.
The customer goes home with 20 more fish heads. Two weeks later he returns very angry. Hey Jimmy he complains, your selling me fish heads for $4 a piece when I can buy the whole fish for $2, your ripping me off!
You see? says Jimmy, you are smarter already.