Tag: sunk costs












A spokesperson for Bupa commented that:






  1. Define sunk costs using some real-world examples.

A key economic principle is that rational decision making requires thinking at the margin. This involves a comparison of the additional (or marginal) benefits and costs of an activity.

An example of such rational behaviour would be deciding to drink one more beer or spending one more hour studying only if the additional benefits were greater than the additional costs. The optimum is where marginal benefit equals marginal cost.

And this applies to firms too. A firm maximises its profits by producing the output at which marginal revenue is equal to marginal cost.

However, a recent book by the American business guru Clayton Christensen argues that thinking in this way can be a problem. A recent article in the Guardian describes a story he tells of the time he refused to play for his university basketball team in a national final which took place on a Sunday and therefore conflicted with his religious beliefs. His decision involved sticking to his principles rather than thinking at the margin. For him, whilst the marginal cost of sacrificing these principles just once may well have been small compared to the resulting benefits, the eventual cost would be much higher.

Christensen also suggests that similar arguments can apply to firm decision making. The above article provides an example he uses of decisions made by executives at the Blockbuster video chain. When smaller rivals started offering movies by mail, Blockbuster instead continued to invest in its existing video store business model. This eventually proved disastrous for the company. The explanation given for this is that building on previous investments made more sense than setting up a mail-order arm which would cannibalise their existing business. On the other hand, an alternative explanation may be that executives at Blockbuster were irrationally allowing sunk costs to affect their decision making.


Clayton Christensen’s “How Will You Measure Your Life?” Harvard Business School, Clayton Christensen (9/5/12)
Clay Christensen’s life lessons BloombergBusinessweek, Bradford Wieners (3/5/12)
Bust Blockbuster goes on the block Guardian, Ben Child (4/4/11)


  1. Can you think of a situation where you have decided to stick to your principles rather than think at the margin?
  2. Why does a firm maximise profit by producing the output at which marginal revenue is equal to marginal cost?
  3. What do you think are the main costs of setting up a mail-order business?
  4. Are these costs mainly fixed or variable costs?
  5. Why is it irrational to take sunk costs into account when making a decision?
  6. Can you think of a situation where you have been influenced by sunk costs?