"A variant of the perfect prediction scam is used by some psychics. If you tell enough clients "someday you will be rich beyond your wildest dreams," then if one of them inherits a great sum or wins a lottery, you may get credit for being psychic."
That one, but slightly different. The psychic example uses the law of large numbers, leveraging statistics. Considering the cyclical nature of the market, statistically you will be right if you predict what happened yesterday will continue today. When it goes up consistently you can keep telling people buy. If it starts going down for a few days you can keep saying sell. Then when it starts going up a few days you can start saying to buy again. And you will be right most of the time. You can use the technical analysis to write off the times you were wrong as "indicators that the market was about to change".
What the real life proof that technical analysis isn't predictive? I'll let this article explain:
"Over the last 15 years, 92.2% of large-cap funds lagged a simple S&P 500 index fund."
Smart, professional investors who do dedicate their lives to research and technical analysis lost to a nearly static list of companies 9 out of 10 times. What's worse? Nearly 2 in 3 large cap funds FAILED in the last 15 years.
"...only 34.11% of large-cap mutual funds that existed 15 years ago are around today. Needless to say, the 65.89% of funds that didn’t survive were mediocre performers when they were merged or liquidated out of existence. "