I disagree with the internet-famous business writer and speaker. You can't blindly ignore sunk costs. You need to consider them to determine your ultimate retur

I disagree with the internet-famous business writer and speaker. You can't blindly ignore sunk costs. You need to consider them to determine your ultimate return on investment, and you should consider them when opportunity-cost doesn't give you more appropriate answer, such as in this example: "Or say you make a mistake and go to the concert instead of selling (those seats are $500 seats now). But Bruce is sick and Manfred Mann is substituting for him. You don't like him so much. But you paid $500 for the seats! Should you stay?" Do you hate Manfred Mann? Will staying improve your feeling of happiness and satisfaction rather than leaving, when you look back on the night in two weeks? I think what Seth is actually tying to say is: "When calculating the opportunity-cost of a decision, your emotional attachment to the money you have previously invested is not generally part of the equation", and "Base your decisions on opportunity-cost, not on sunk costs", which is sound. Finally, will spelling the word on the sign correctly actually help the convenience store owner? Do people visit convenience stores based upon branding and proper lettering, or do they visit them because they are available or convenient? Your sunk cost has gotten you a sign. Is there another investment with a greater return than redoing the sign?