Author Margie Warrell recalls keeping on wearing a pair of designer shoes even though they made her feet ache because she had paid a lot for them. She says she was thinking “I need to get my money’s worth!” She tells this story as a warning against “sunk-cost bias”.

a. What type of cost is expenditure on shoes?

b. Why is the price paid for the shoes irrelevant to your decision about whether to keep on wearing a pair that cause pain?