More true than you think.
A few years ago I ordered a book called something like the "Index Investment Strategy" that "guaranteed" outsized gains.
In researching their claims, they were indeed buying the low one day, and selling the high the next day when a stock was announced that it was going to be added to a major index.
I'll never forget calling the writer/publisher, and after pointing out to him that his claims were fraudulent and impossible to achieve, he guaranteed that "thousands of people were happy with his system." and had no problem buying the low and selling the high the next day.