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is because markets are anti-inductive. they correct for 'knowledge' of future price information. so you not only have to see the trend forming from regular trading, but anticipate the actions of all of the others who see the trend as well.
Which leads to the conclusion: what technical analysis claims to achieve is pointless.
We can safely skip the question if it's an intentional deception or mystification, it is sufficient that it is a mystification, by its nature.
"Technical Analysis".
The whole way it is named and is presented by it proponents suggests a degree of precision and rationality which in reality isn't there.
The first thing when you start learning math is to prove the necessity of new terms and laws you introduce, and to prove that any construction you create actually delivers what you claim it to do. The first thing when you start learning engineering is to judge the accuracy and error level of your measurements. And you learn that it is your duty to prove that an claimed effect actually exists.
Note that the point is not that you can generate an effect, but the point is to prove that a proposed method is necessary to yield the prediction, understanding or effect.
It is possible to create a stunning construction out of mathematical methods, which might be even hard to grasp and to execute, while it has actually no relation to either the nature of the mathematical objects, or any relation to the observable parts of nature or society. Such construction might be a piece of art, it is not math, nor is it analysis, nor is it a precise method.
It might well be that all the stunning constructions, formulas and indicators of technical analysis have only weak or no relation to the real phenomena, and that any observed "benefits" from applying technical analysis are actually due to the experience of the traders and due to just statistical effects. This possibility has not been sufficiently addressed with due diligence.
Thus the verdict of a mystification and self-deception.
Maybe (I hope so) current and future research will give us reliable methods and a positive proof of the effectiveness of such methods. Maybe this verdict can be lifted at some point. But we aren't there and we need more critical thinking and questioning of our own actions.
No doubt any effective trader has heuristics and guidelines.
But if it is experience, then please call it experience.
If it is gut feeling then please label it as gut feeling.
If it is a craftsmanship, gained by training and apprenticeship, then please call it so, and be proud of it.
But don't label it with anything associated with exact methods, science and technology.
And stop that math and numbers bullshit for things which have an prediction error of +- 100% and only apply in 3 of 5 cases. ;-)