The average lifespan of a friendship? 10 years. Here’s why.

This is the psychology of why friendships (and marriages) fail.

  • Some friendships last a lifetime, but most have a lifespan. In the U.S., best friends tend to last for 10 years on average, says Nicholas Christakis.
  • In friendships, one person may begin to defect or "free ride", which causes the other person to choose between cooperation or defection. People tend to choose the latter so they won't be taken advantage of.
  • A certain amount of social fluidity, taking a breather from a friendship, can actually make a friendship last longer.
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