Or why is it so hard to prove that winning methods works and losing methods sucks.This article serve to highlight what i think is the fundamental problem of investing. It is probably also the source of the biggest fallacy currently circulating around the investing world. (the fallacy that past performance is a definitive indicator of future performance)
The problem can be stated simply as such:
Failure to take into account the existence of probability.
THE CULPRIT"
It made money, therefore it works."
Shockingly, I have heard this being used as a justification for investment decisions. The issue with this is: past results tells us nothing about future performance. To see why, imagine an asset that has performed well in the past. To many investors, this will be deemed as a "good investment" simply because of its history. However, if we stop to think for a moment we might realize that there might have been two possible scenarios:
1) The asset is good and therefore past performance is good.
2) The asset is bad but performed well in the past by pure chance.
How can we tell which one is true?
Even if there are "good reasons/fundamentals" for the asset to perform well, how do we know if these reasons and/or fundamentals are not painted on after the fact? What if a good asset, despite having good fundamental attributes, continue to perform poorly due to chance? Is it a failure of our fundamental criterion or is the asset "bad" to start with?
Can we ever really tell?
STATISTICS 101To illustrate how probability distorts investing decisions in the real world, lets suppose we have a very lousy mutual fund manager. Lets call him Bob.
Bob really sucked at fund management: 70% of the time, he end up losing money overall for the year. 30% of the time, he beats the market for the year. Would I invest any money in him? No way!
However, Bob beats the market 30% of the time. This means that he has a 0.81% chance of making money 4 years in a row. Out of 125 fund managers like Bob, there is likely to be 1 who shows a stellar track record of 4 consecutive winning years.
Investors might then see advertisements that say:
Make your fortune with Bob's Fund, the premium investment vehicle with an excellent track record of 4 consecutive market beating winning years!Will investors who placed their bets on Bob necessarily lose in the coming year by virtue of him being a bad fund manager? It need not be so. Bob still have a 30% chance of making a profit.
And then advertisements will say: "
5 years of excellence in fund management".