you did ask the personal question "How do you know?" and I interpreted this as your wondering how I, James Miller, acquired my knowledge of financial markets.
A bit of miscommunication, then, my question referred to the quote directly preceding it which is
since you would likely conclude after lengthy study that yes, one should just buy index funds
I meant "How do you know that I would likely conclude after lengthy study that yes, one should just buy index funds?"
If you read LW you are likely the kind of person who, after massive study, would agree with economists on microeconomic issues on which most economists agree because microeconomics is really math and logical reasoning applied to human behavior and economists are, relative even to the LW population, good at these things.
Another month, another rationality quotes thread. The rules are: