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There is no prediction that is 100% accurate, so the results of technical analysis will be subjective depending on how traders interpret price history which they then process into an entry signal. Actually, it is not a matter of trust but of possibility, in fact traders are very flexible to change the type of analysis used if it is not profitable enough.
It's true that what you say is that there are no 100% accurate predictions, it's just that perhaps by predicting them we can understand a little of the developments that are occurring.