Why Jack Reacher (probably) can't learn probability.

Okay, now I need to start this post by saying that I LOVE Lee Child’s Jack Reacher series. I own them all, have read each multiple times, and buy the new ones as soon as they are published. I am not going to be making any criticisms of someone who writes far, far better than me. I will touch on some ideas relevant to the teaching of probability though, and how Reacher sometimes helps me make a point in maths education lectures.

Teaching Probability and Student Intuition

I was thinking about this recently as I’m just about to begin my Statistics and Probability curriculum and pedagogy course for students doing a Bachelor of Education degree. One of the wonderful articles which it is very important for students to read is “How Students Learn Statistics” by Joan Garfield. One of the big points which I take from this article is that children bring prior experiences and intuitive ideas about randomness and probability, which actually impede their understanding of probability. These intuitions are pervasive, and are more a function of being human than of maturity.

Adults continue to use these ‘heuristics’ or ‘biases’ as described by Kahnemann, Slovic, and Tversky in the 1970s and 1980s when interpreting statistical ideas. (The book Thinking, Fast and Slow by Daniel Kahnemann (2011) explains really well the development of these quick, easy rules of thumb through evolutionary pressure.)

The Equiprobability Bias

One of the biases which causes difficulty for students is the equiprobable bias—the assumption that all events have an equal chance of occurring. There are several possible foundations for this belief developing in students, one of which is the examples presented to them in school, all focusing on the “fair die,” “fair coin,” or “balls drawn at random from a bag,” where the choices are all equiprobable to make the examples simpler.

This particular bias was examined by Marie-Paule Lecoutre in 1992 in the article “Cognitive Models and Problem Spaces in ‘Purely Random’ Situations.” The experiments conducted by Lecoutre also illustrated a common theme about these heuristics, biases, and assumptions: formal education in probability allows students to interpret the situation correctly, and calculate the correct answer when it is presented as an obviously probabilistic maths problem, but they still fall back on their heuristics and quick thinking when the question is posed in another context.

A very powerful quote from this article is:

“It is interesting to point out here that even a thorough background in the theory of probability did not lead to a notable increase in the proportion of correct responses. These results show how highly resistant the equiprobability bias is, and they are quite consistent with the idea recently brought up by Fischbein (1987), who claims that intuitions (correct as well as incorrect) are often very robust, ‘being deeply rooted in the person’s basic mental organization.’”

What has been shown to be effective is for students to take part in a number of learning experiences which directly address and contradict their pre-existing biases.

Jack Reacher and Fifty-Fifty Thinking

So, what does all this have to do with Jack Reacher? In the books, Reacher frequently interprets uncertain outcomes as “fifty-fifty” chances, regardless of context. For example:

• In The Midnight Line, he sums up a situation with a simple line:

“Fifty-fifty right or wrong. Not bad odds.”

This shows Reacher equating uncertainty with a coin toss—quick, decisive, and pragmatic.

• In Never Go Back, he applies the same thinking to a sequence of events:

“Would Susan Turner get a new lawyer that afternoon? Answer: either yes or no. Fifty-fifty. Like heads or tails… Four correct answers in a row were a six-in-a-hundred improbability.”

Here, Reacher treats multiple events independently, assuming each is an even chance. It’s a perfect illustration of the equiprobability heuristic—how humans often oversimplify uncertainty by assigning equal likelihood to outcomes.

• Later in the same book, he reflects more philosophically:

“Was he a drone, or was he ahead of the curve? Fifty-fifty, Reacher thought, like everything else in the world.”

Reacher’s fifty-fifty thinking isn’t just about practical decisions—it’s a lens through which he interprets the world, echoing the intuitive heuristics that can trip up students learning probability.

Literary Device or Cognitive Bias?

To be fair, it might be said that the author is actually using this as a literary device to illustrate beliefs of the character—he is pragmatic, and when faced with uncertainty is willing to use heuristics to act quickly in high-stakes situations, and guards against overthinking when information is not available. It keeps Reacher mentally agile, ready to adapt as new information arrives.

Across literature, the equiprobability assumption—whether explicit or implicit—helps convey characters’ uncertainty, heighten tension, and propel narrative choices. It mirrors how real humans process ambiguous situations with limited info.

Perhaps the author is using this cognitive bias in a clever and subtle way, but it always grates when I read one of these lines, and the irritation takes me out of the immersion of the story. At least it gives me a go-to example when discussing in class the kinds of human thinking which makes teaching probability difficult.

Footnote:  For a larger collection of Reacher’s fifty-fifty quotes, see Appendix A

Quiz: Which Sum is More Likely?

You roll two standard six-sided dice. Which sum is more likely to occur?

1. a) 10
   b) 11
   c) They are equally likely