We perceive value based on outside factors as a mark of reference. Taking up your example, you evaluate a t-shirt based on what was important to you at that time, bears, so a t-shirt = 5 beers, however now you may value other things and let’s say you would think 1 apparament=3cars. Oh, and why you would even need a car? Because your friends and colleagues have one and it is a symbol of success and a way to values your worth based on the car’s brand.
Kudos for this article, is very well written.