Literally everywhere for the past years I see the advice to invest in index funds - the only question I have is what happens when a critical mass of people do just that? Wouldn't that influence the market in some way?
(...which is a common counter-argument for the markets being efficient. The reasoning behind passive investment is that, net of fees, it's difficult to out-perform the market although of course, everyone can't outperform the market because everyone collectively IS the market)
These days I think in reality most people who have been into indexing for a while give themselves a bit of play money to invest in something more speculative.