Offer your thoughts or opinion on the input financial query or topic using your financial background.

At what point do index funds become unreliable?
private investors that don't have the time or expertise for active investment.  This may be known as every private investor. An index fund ensures average returns. The bulk of active trading is done by private institutions with bucketloads of experts studying the markets and AI scraping every bit of data it can get (from the news, stock market, the weather reports, etc...). Because of that, to get above average returns an average percent of the time, singular private investors have to drastically beat the average large team of individuals/software. Now that index ETF are becoming so fashionable, could there be a tipping point at which the market signals that active investors send become so diluted that this "index ETF parasitism" collapses? How would this look like and would it affect only those who invest in index ETF or would it affect the stock market more generally? To make this question perhaps more on-topic: Is the fact (or presumption) that index ETF rely indirectly on active investment decisions by other market participants, as explained above, a known source of concern for personal investment? This is a well-covered topic. Some people think this will be an issue.   Others point out that it is a hard issue to bootstrap. I gravitate to this view. A small active market can support a large number of passive investors. If the number of active investors ever got too low, the gains & likelihood of gains that could be made from being an active investor would rise and generate more active investors. Private investing makes sense in a few cases. One example is ethics. Some people may not want to be invested, even indirectly, in certain companies.