Sunk Costs: There’s No Crying Over Spilled Milk

"You and I could be in the identical situations but appraise the costs and benefits differently, and thereby end up making different choices. Economics says nothing about what should count as a benefit or cost, only that, whatever one chooses to count as benefits and costs, one should focus on the additional, or marginal, benefits and costs of a particular option and go with the one delivering the greatest net marginal benefits."