Hide the math

People don’t like doing sums, and so if you show them answers rather than the workings, they’ll be inclined to believe you – even if the answers are only partial.


  • Penny auction sites (win an iPad for just $5) don’t make it clear that the “winning price” is what participants pay in addition to the number of bids they’ve made. Each bid increments the price by one penny, but costs 50 cents. Losing bidders don’t get their bid money back.


A couple of interlinked psychological and economic principles are at work here: irrational escalation of commitment and the sunk cost fallacy (a form of loss aversion).

How to hide the math

  • Make the arithmetic associated with your product hard to perform.
  • If possible, add confounding factors such as urgency, excitement or competition so that users focus on these rather than the math.
  • Use familiar terminology, but make the words mean something slightly different. For instance, in traditional auctions bids cost nothing unless you are the winner, whereas in penny auctions, bids cost money the moment they are placed.
  • Automate the process of spending money wherever possible so that it slips out of awareness for people.
  • Provide tutorials that explain how easy the process is without pointing out the implications.
  • Use tokens to remove the sense of spending real money
  • Make a clear statement about the value of the item being auctioned/sold, but neglect to mention associated costs.
  • Keep people interested until they reach the point of irrational commitment by having sufficient cost sunk in the item. From then on, psychology will do your work for you.