A woman wants some potatoes for the meal she is cooking, so she sends her husband to the marketplace to buy potatoes. As he walks out the door, she calls after him "be sure and get a good price."

So all the way to the marketplace, the man is thinking about potatoes and what he'll have to pay. If he buys the very best potatoes, he knows he'll have to pay more than if he buys lesser quality potatoes. On the other hand the lesser quality potatoes are just that - not so good. In fact he knows he'll have to be very careful in buying other than top price potatoes because the seller might try to stick him with a bad potato, even a rotten potato.

When he thinks of some one cheating him by giving him a rotten potato, he gets really mad. "Why do people have to be so greedy as to stick me with a rotten potato?" Just at this point he reaches the stall of the potato seller and screams at him "You can keep your rotten potatoes!" and walks off.