The key difference is that Harmonic patterns identify low-risk/high-probability reversal trades, and clearly define where to put a stop-loss. The success rate of harmonic patterns is well documented and has been established for over 75 years.
Whereas chart patterns are largely breakout trades. And that's the problem. Only about 30% of breakout trades work out, and they are notoriously difficult to trade successfully at the best of times.
For more information on why breakout trading is difficult and generally unsuccessful - see Sam Seiden's Video on Breakout Trading.
Having said that, many (non-harmonic) chart patterns are classified as "reversal patterns" - not "breakout patterns". Why? They mean that the pattern indicates the reversal of the previous trend.
However, the usual way to trade them is as a "breakout" trade. Take the "Head and Shoulders Tops" pattern as an example:
It's classified as a "short term bearish reversal" pattern by Bulkowski and others, since it indicates a reversal in the preceding trend. However - you trade it is as a breakout across the neckline support level. (Hint: the clue is in the word "breakout").
Now imagine, for a second, there was a harmonic pattern signal for a high probability/low risk short trade at the top of the head (or even the top of the right shoulder). A harmonic Butterfly, or Crab pattern may well identify such an opportunity - in which case you would have been in the new trend far earlier than all those trading it as a breakout.
The number of (non-harmonic) chart patterns is overwhelming - Thomas N Bulkowski's very comprehensive "Encyclopedia of Chart Patterns" has over 1000 pages listing more than 50 such patterns. That's a lot to try to remember, I think you'll agree. In comparison - I trade just 4 harmonic patterns.
You can see what I mean by browsing Bulkowski's book here: (but don't spend too long in there - hurry back here to continue to learn more about harmonics!)
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