9 Vignettes in three Acts about everyday Life and logical Fallacies

Digital development realities, as told by logic and the errors in our reasoning

Act 1: The setup

Answering an easier question

An investor thinks about a new investment, and if he should buy stock of the Ford Motor company. He thinks so, because he thinks Ford makes nice cars, and he is sure they will sell well.

This is you, asking yourself what the client wants. And not what the clients customers need.

The Dunning-Kruger Effect

Someone with no education in constitutional law repeatedly weights in on what „freedom of speech“ really means in heated online discussions.

This is you, talking expertly about something you researched the day before the presentation.

Act 2: The confrontation

Law of small numbers

A traveller comes into a foreign town. The first ten people she sees are all children. She concludes that there are no adult residents in this town.

This is you, asking your friends why they use certain products.

Correlation does not imply causation

A scientist wants to know what causes cancer. He notes that cancer cases are rising, just like the sale of oranges. He concludes that oranges cause cancer.

This is you, reaching qualitative conclusions from your quantitative research.

Illusion of understanding

Someone writes a success story about a famous company and its founders, explaining all positive outcomes with the founders’ genius, while ignoring all negative outcomes.

This is you, building your product strategy by telling an intricate story about complex consumer behavior, based on two app usage metrics.

Regression to the mean

A man has tremendous back pain, and visits a doctor. After that visit, his back pain got better. The man is convinced that the doctor treated his back pain well.

This is you, ‚fixing‘ various issues in a website that is performing much worse than expected without a clear understanding what is going on, crediting your swift intervention with any performance improvements.

Act 3: Resolution

Hindsight bias

A manager is justifying her gut-based and risky decision by its positive outcome.

This is you, sending that „I told you so“-mail to all other participants of that strategy meeting, not bothering to check if your other predictions were correct as well.

The Texas sharp-shooter

A man stands in front of a barn. He fires his rifle multiple times into the barn. Then he walks over, and draws a big target circle around the bullet holes.

This is you, defining your metrics after your product launched.

Survivor bias

An engineer examines bombers returning from combat. She analyses where the bombers have been hit and reinforces these areas, not realizing that in these areas, the bombers are already strong enough.

  • This is you, trying to learn something from a TED talk about success.*


When it comes to logical thinking, Digital Product Development is not free from sin. Even if we follow best practices and design processes, errors in judgement can creep in through the cracks in our daily routines. We have to move and think quickly. In these fast-paced environments, it is often difficult to think clearly and critically. Critique takes time, something that seems to always be in short supply. The above list is of course a lighthearted commentary on the things we often see in our projects. But it can also be a handy checklist for you to consult from time to time.


Inspiration and examples are taken mostly from Daniel Kahnemans ‚Thinking, Fast and Slow‘, and David McRaney’s ‚You are not so smart‘ podcast and book.

If you want to read more about logical fallacies, you can get a good summary and various pointers from this wikipedia overview.

The header image is a screenshot from Monty Pythons Philosophers Football.