[Tloewald]

There's a ton of evidence we aren't doing what's in our best interest at minimum a significant minority of the time. In any event, the claim of economics isn't that people act in their best interest, but that they try to maximize happiness* -- whatever that is (it's rather recursively defined -- happiness is produced by voluntary transactions, which in turn are voluntary because both parties believe that the exchange will make them happier).

* or whatever it is makes transactions pareto optimal.

Meanwhile, behavioral economists have shown humans aren't even great at pursuing happiness; perhaps they have reached their high water mark, but they're certainly not completely wrong.