Bunge, a grain dealer, contracted with Recker, a farmer to purchase 10,000 bushels of soybeans at $3.35 per bushel. The contract did not specify where the beans were to have been grown, except that they were to be grown in the United States. Because of crop failure, Recker was unable to deliver the beans, even with several extensions of the deadline. Finally, Recker admitted that he could not deliver, claiming impossibility of performance. In the meantime, the market price had increased from $3.35, the agreed price, to $5.50 at the time of delivery. Bunge sued for the difference between $3.35 and $5.50 the price at delivery.

Explain the principle of law that is being observed?