It’s the invention of the test prep industry so they can sell you their “miracle cures.” This isn’t to say that all test preparation companies take this line. A few companies, Bell Curves among them, pride themselves on providing test prep that speaks to the knowledge, insights, and strategies needed to conquer the test, rather than play into the notion that these tests are designed to trick test-takers. My gripe with the other, more popular position is that it seems designed to make the test out to be a big scary mysterious unknowable boogie man designed to jump out of the dark and bop the unwary, and thus force test-takers to get help from someone else to defeat the unknown and unknowable. However, if the test is just a test, a test of content, a test of information, a test of factoids presented in a very particular way, then you might be able to prepare on your own. It’s got to be easier to sell a course or tutor if “only SAT experts” have the key to this very special lock.
Don’t believe the hype!