Why is there a discrepancy between long-term and short-term effects of a change in demand?

Question

Quizplus · Accepted Answer

Short-term and long-term effects are different because there is a cost associated with adjusting to the market. For example, if a farmer must choose between growing corn or wheat, he or she will check prices before buying seeds. But a farmer who has already bought seeds would face a large loss by throwing them out and buying seeds for a different crop.

Why Is There a Discrepancy Between Long-Term and Short-Term Effects