2 paragraphs about a decision you made in the past that you now regret

In at least 2 paragraphs write about the following:

Think about a decision you made in the past that you now regret. Describe the decision you were making in terms of marginal benefit versus marginal cost (Economic Decision Rule) and describe why you undertook that decision.

In terms of marginal benefit versus marginal cost, describe why you have now come to regret that decision