Here is an example of the black magic that you can sometimes achieve with Fibonacci retracements.
Lets go back to June when the Russell 2000 small-cap index looked like it was going to the moon during a bear market rally (click to enlarge):

Now, suppose you wanted to short that crazy chart without having your eyes gouged out with a hot poker. How do you pick an entry point? One way is with a Fibonacci retracement. Using TradeStation’s fib tool, I have drawn a retracement from point A to point B. I chose point A because that was the cliff that prices dove off of. Notice that one of the magic fib levels, 161.8% (blue line) happens to match up with the peak:

And that was the exact point where the rally topped out:

Pretty amazing, right? Of course, prices could have moved up to the next fib level. Nothing is guaranteed in the stock market. But Fibonacci levels give you hints about price levels that may turn out to be important.
Learn more with The Harmonic Trader, a free book that you can download.
Note: I tweaked TradeStation’s Fibonacci tool to add the extra levels recommended in the book.