Note that this is not to say that I (or anybody else) engages in strict, robot-like, mathematical optimization of all transactions to ensure that our best interest is served down to the .00000000000001th place. We, as human beings, employ satisficing[1] for a lot of our decision making. But the fact that I buy from Amazon when I could save 50 cents by buying from Walmart instead, or that I tolerate Amazon showing me a few ads when I'm shopping, is neither here nor there.
This is a fallacy. People often engage in transactions that aren't in their interest- believing in the moment that they are. Or said another way, there's a difference between long-term interest and short term interest, and people often don't see their long-term interest clearly. Or said still a different way, there's a big difference between happiness and pleasure, and people sometimes engage in pleasure in detriment to their happiness (roughly from the Dalai Lama).
I'm not talking about the 10^(-14). I'm talking about real decisions where there is an information asymmetry. And meth.