Eli Bendersky's website In some American Indian reservation, the natives asked their chief about the upcoming winter - will it be cold or mild. The chief had no idea, but to look knowledgeable he told them that the winter will be very cold, and they should hew and store as much wood as possible.
Some time later, the chief felt uncomfortable about telling this to his people without knowing, and had doubts, so he called the meteorologic service. They told him that the winter will be cold, so he felt a little calmer and told his people to store even more wood for the cold winter.
A few weeks later he called the meteorologic service again and got the same answer.
When he called the third time and was told that the winter is going to be very cold, he asked the weather-man what data he relies on.
"But that's obvious" said the weather-man "the natives are cutting down trees like crazy !".
Ahh... so true, so true for the stock market.