Query: Dalbar: How can the average investor lose money?

Relevant passages:
 <=SEP=> "It appears that there's a confusion between the different types of average. Saying ""the average investor"" generally means the most common type of small-scale unsophisticated investor - the mode (or possibly median) investor. However, while this class of investors is numerous, each of them has assets that are quite small compared to some other types of investors; and the market average performance is determined proportionally to the amount of assets held, not to the number of holders; so the performance of large investors ""counts"" that much more. For any measure, the mode of performance can be (and often is) different from the mean performance - in this case, Dalbar is saying that the most common results are lower than the (weighed) average results."

 <=SEP=> "How is it possible for the average investor to underperform the market? The ""average"" investor probably makes some bad decisions. You also might need to take transaction costs into play (including borrowing on margin), so that there's a natural ""erosion"" of returns across the market.  Meaning if transaction/borrowing costs are 1%, and the market return is 5%, the ""average investor""  Alternatively, if by ""average"" they mean the average of the population, not weighted by amount, it's plausible that the mass of smaller investors perform slightly worse than the smaller number of large investors (and have larger relative transaction costs), thus having a lower average on a per-capita basis. Doesn't the fact that investors can consistently underperform the market by making poor decisions, imply that an investor could consistently outperform the market by making the opposite decisions? No.  If my investment decisions cause me to earn only a 10% return compared to the ""average"" 12% return, then making the opposite decision will cause me to lose 10%, not to make 14%."

 <=SEP=> I think you are mixing two different concepts here. The average investor, in the quoted reference, means an average single investor like you or like me. the average investor consistently under-performs the market. However, you then ask the question and you seem to refer to all investors as a group; individuals, institutions, investment banks, et al. since together, investors own 100% of the stock in every company? Every investor could match the performance of the market easily and at low fees by simply buying an S&P index fund and holding it. In fact, some investors can even beat the market with the addition of some stocks. Here is the ten-year chart of Berkshire-Hathaway B compared to the S&P 500.   There are other examples. However, few of us have the discipline to do so. We read questions here every week about the coming turbulence in the market, about the next big trend, about the next bubble, etc. The average investor thinks he is smarter than the market and buys on a whim or sells likewise and misses out on the long, slow overall growth in the markets. Finally, the title of your question is “Dalbar: How can the average investor lose money?” I doubt that the average investor loses money in the past several years. Not making as much money as is easily possible is not at all the same as losing money.