A salad and doughnut cost £1.10.
The salad costs one pound more than the doughnut.
How much does the doughnut cost?
Well that’s easy! It’s 10p.
The answer is actually 5p. If the doughnut costs 10p, then the total cost will be £1.20 (10p for the doughnut and £1.10 for the salad). If you do the math you will see the easy, intuitive answer of 10p is incorrect and 5p is the correct answer. And if you did indeed get it right, you probably had to resist this initial incorrect answer which came to your mind.
This is a perfect example of your System 2 listening to your System 1. Why? Because it is the easy option. Kahneman and colleagues have done work to argue that System 1 and 2 have personality traits and although System 2 is logical and reasoning, it can also be lazy and rely on System 1 in certain situations. We see this also when System 2 is busy or depleted, and this has a direct relation to the food we tend to go for.
What happens when System 2 is busy?
Previous psychological studies have highlighted that when someone is faced with a cognitively demanding task and given temptation, they are more likely to give in to that temptation. For example, if you are asked to remember a string of numbers, and during this time you are offered a salad or an oozing chocolate cake, you will almost always pick the cake. But why is this the case? Baumeister and colleagues named the phenomenon ego depletion; where an individuals self-control or effortful will becomes tiring. As a result, as time goes on you are less willing to exert the same effort to maintain self-control for another task or challenge. Furthermore, it is clear that mental, emotional and physical functions all use the same mental energy source. As a result, an emotionally draining encounter can make you feel less willing to do the next physical task.
Baumeister, R. F., & Vohs, K. D. (2003). Willpower, choice, and self-control.
Baumeister, R. F., Vohs, K. D., & Tice, D. M. (2007). The strength model of self-control. Current directions in psychological science, 16(6), 351-355.
Kahneman, D. (2011). Thinking, fast and slow. Macmillan.