Ariely points out that almost all of our decisions are made for us due to the way they are presented. We often gain illusions from our choices that greatly influence the things we chose.
First, Ariely shows some examples of visual illusions such as this table or this cube:
An example of one of these "cognitive illusions" is a study on advertisement customers of the Economist. When presented with the choices of:
Print only: $89.00, Web only: $125.00, or, Print and web: $125.00, the most popular choice was Print and Web, while no one chose web only, and few chose print only. This trend occurred because the customers saw that print only had the same price as print and web together, so they chose to buy print and web because it appeared to be a good deal. Why settle for one when you can get both for not paying more?
Interestingly, when the web only option was removed, more customers chose print only than print and web together. When the comparison was gone, they chose the cheaper option. I found this point extremely interesting because, I know I have often fallen for tricks like this. Judging something based on what you have to compare it to is in our human nature, but it often hinders us rather than helps.
Illusions like these show us how our decisions are already made for us because what we really want is not what we consider in our decision making. We consider instead how the options are presented to us and make comparisons to alter our decisions.
I personally believe this relates to literary tragedy because the tragic characters often fall to cognitive illusions. For example, It has been foretold that Oedipus would kill his father and marry his mother. This "pre-decided" fate influences all of Oedipus' decisions so that it eventually becomes true.