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  • Bitesize Behaviour Host

Series 1, Episode 3: Mental capacity

In the last episode we started to look at the brain. We looked at fear and we learned a simple fact, that people really struggle to make decision when something is complex.

The reason behind this is that complexity requires slow, deliberative thinking and as we’ll explore shortly, our mental capacity to work through complex decisions is really limited.

Scientists used to believe that people made decisions in a rational way. What this means is that as long as we are presented with all the information we need, we can process everything that is in front of us and from that make a decision that is the best option for us.

But that’s not how our brains are wired to naturally work and scientists have now proved that presenting people with every piece of information they may need to make a decision can actually be counter-productive. And evidence also points towards two other important areas that we need to understand.

The first is what is know as our capacity for thinking, and the second are the two types of thinking we use. We’ll look at that in the next episode but in this episode, but for now let’s focus on our capacity for thinking, and let me try and show you exactly what I mean when I say our capacity for thinking is limited.


Research on how the brain works shows that the amount that we can think about at any one time, is severely limited. And I want to try and prove this point to you in a fun way. We’re going to play a little game. Please play along as it will show you how, what we’re talking about here, plays out it real life.

OK. I'm going to show you three maths questions. All you have to do is try and solve them in your head. No writing anything down... after all we are testing your capacity for thinking.

Here we go. What is:

2 + 2

78 + 93

67,876 + 92,823

Now the first question is dead easy. The second one will have seen you slowing down a little in order to work the answer out. The third one is very, very, very difficult to do in your head. But why?

Well, what this really simple exercise shows us, is that when we need to engage in proper deep thinking, in this case adding two five digit numbers together in our head, or more to the point, when we have to slow down and really think hard, it is severely limited - not only in terms of the brain’s capacity to store the relevant information (2 five-digit numbers), but more so in terms of the mental operations it has to go through at the same time - adding them together.

But this does beg an obvious but important question. If people potentially struggle to remember 2 five-digit numbers forget being able to do add them together, what’s happening in our heads when we need to make complex or difficult decisions?

We know that thinking hard is really hard to do and if we have complex problems that we need to solve, it doesn’t take long before we run slap bang into difficulty. But this doesn’t mean that we stop making decisions. Of course not! We can’t just stop because it’s difficult else we would never make a tough or complex decision.


What happens is our brain's evolution comes to the rescue with a couple of really clever tricks that help us make decisions, whilst at the same time, bypassing as much complexity as we can.

We’ll look at these two decision-making tricks over the next two episodes, starting with how we have learned, with amazing efficiency, to simplify our decision making process, and in order to understand how this simplification works, in the next episode we will look at the two types of thinking we use when we need to make a decision.