The Detective says to Inspector Dalgliesh

So, the detective says to Inspector Dalgliesh, “Don’t worry sir, I’ll keep an open mind.” Dalgliesh says to himself “No he won’t, he’s already made up his mind.”

The little scene for one of P.D. James’ crime novels has been on my mind. What does it mean to have an open mind and why is that so important?

There are plenty of books and TED talks that you could read or watch but they may get you more confused than you need to be. (By the way, confusion is not a bad thing if you use it as an impetus for critical thinking.)

Let me suggest three key reasons for the importance of an open mind.

  • We succumb to the “fallacy of the excluded middle.”
  • Our assumptions may be wrong or degrade over time.
  • “Resulting” may lead us astray.

Fallacy of the Excluded Middle

Let me present a false dilemma: Donald Trump is a great president. Donald Trump is a terrible president. Pick one!

If you chose one or the other, you let yourself succumb to the fallacy of the excluded middle. A person with an open mind should avoid the extremes when plenty of middle ground is valid. But if you let dogmatism control your thinking, only the extremes exist. Either you love our president, or you hate our president. Now be honest with yourself, isn’t he “somewhere” in the middle?  (By the way, I could have done this a few years ago for Barack Obama. Same issue)


I’ve taught workshops focused on strategic thinking for a long time and I generally refer to faulty assumptions as “the high blood pressure” of strategy. You don’t know you have high blood pressure until you check it or until you’ve had a heart attack or a stroke. You don’t know your thinking assumptions are faulty until someone points them out or until you make a bad decision.

Here are a few assumptions we made for a while:

  • China only knows how to make cheap stuff; they have no innovation. Oops, they just landed a rover on the dark side of the moon. Maybe they can innovate.
  • Multi-tasking is a valuable skill that boosts individual productivity. Oops, multi-tasking is actually multi-distracting and damages individual productivity.
  • “Our brand is old, established, and our customers love us!” Oops, that was a quote from a leader at Sears when I did some work for them in the 90s.


I found the term “resulting” in a wonderful book written by the (former?) professional poker player Annie Duke. [Side note: I really like her book Thinking in Bets: Making Smarter Decisions When You Don’t Have All the Facts] “Resulting” is the human tendency to equate the quality of a decision with the quality of the outcome. We get a good outcome and we think that our decision making (hence our thinking) was good. We take all the credit and push lady luck to the side.

Unfortunately, it’s not just poker players who fall into this trap.

  • The engineers at NASA launched the space shuttle Challenger because previous decisions to launch with a faulty O-ring resulted in successful take-offs.
  • Early investors in Bernie Madoff’s Ponzi scheme made money and considered themselves financial geniuses and brought their friends into the mess.

This has been a quick excursion into the challenge of thinking with an open mind. Remember:

  • We don’t live in a black & white world. Grey exists, and you should look for it.
  • Bad assumptions usually stay hidden until it’s too late. Bring them out into the open.
  • Luck exists. Don’t evaluate your thinking skills on just your results.

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