Very clever people are likely to fall into the rationality trap. Because they are used to winning discussions with good arguments. 

The conviction grows in them that everything can be rationalised. The "right" strategy? A question of systematic analysis. The best business decision? Likewise. 

A high IQ is demonstrably helpful in getting ahead in life. What's more, IQ is the best predictor of success that psychology has to offer. 

People caught in the rationality trap do not understand that there are limits to rational thinking. Yet the world is bursting with irrationality. But they hide themselves quite cleverly, just like the blind spots in our field of vision. The dangerous thing about the blind spot is not that you can't see anything there. It's that you can't see that you can't see anything. The blind spot is added to our field of vision.

That is why the limits of rationality cannot be approached in a straight line. Otherwise the blind spots disappear and everything seems logical. However, a few simple mental exercises ruthlessly demonstrate the limits of rationality. Read on at your own risk.


The amount of available information is approaching infinity. The processing capacity and time is limited. This alone shows that rationality is possible in theory - namely to systematically organise all available information. In practice, however, there is not enough time.

What's more, the world doesn't care whether something makes sense. Just because things happen simultaneously and are apparently interdependent does not mean that they do so effectively. A school example is that the stork population correlates with the birth rate. Statistically significant and perfectly verifiable. (The moderating variable here is urban-rural: there are more storks and a higher birth rate in the countryside)

First and second order observation

Until the middle of the last century, the scientific world was simpler. People observed things, described them and that's how it was. Then we realised that the observers sometimes influence what they observe. Double-blind studies are one answer to this in clinical trials. In many places, however, this is not possible. A few examples:

  • How does a manager's conviction influence the leadership situation? For example, there are studies that show that classes make much better learning progress if the teachers are convinced that their class is of above-average intelligence. This also works if the pupils are randomly selected - so the information about IQ is not correct at all!