Or that people are actually, as has been demonstrated in any number of ways, irrational. The idea that perceiving irrationality means there is something wrong with your world view rather than that there is actual irrationality in the world is somewhat odd.
In a fictional world, an envelope costs $1, a piece of paper costs $0.50, and a stamp costs $0.50. In total, a full letter costs $2. You know that anyone on the street would be willing to buy each of those items at the component price. Would you not agree that seeing all 3 sold as a bundle for $1 would be irrational?