“Rational decision making requires you to forget about the costs incurred to date.”

Why it was said

Rolf Dobelli closes his short chapter on the sunk cost fallacy in The Art of Thinking Clearly with this sentence. The chapter describes how people keep investing in projects, plans and commitments because of what they have already put in, not because of what lies ahead.

What it actually means

Money, time and effort already spent are gone whatever you decide next, so they should not weigh on the decision. Yet they do, because stopping feels like admitting the spending was wasted. Dobelli's line is blunt: the only question that matters is whether future costs and benefits justify continuing. That is easy to say and hard to do, since a sunk cost is often tied to our pride or to a promise we made in public. The practical move is to imagine you are starting fresh today, with no history, and ask whether you would begin this project now. If not, the past is no reason to go on.

How to use it

1. 1For one ongoing project, write "If I were starting today, would I choose this?" and answer honestly.
2. 2Separate what is already spent from what is still to be spent, and decide only on the second list.
3. 3Set a review date and a stop condition before you start your next big commitment.