Its purely a theory. But all the characteristics and outcomes of the process of learning from reputable and honest experts in trading bear it out. I have not heard any trading expert share this theory, but they obviously wouldn’t be doing self-defeating like that.
So, when you learn about trading from a reliable, honest and expert source, there are 4 possible outcomes for the student -
a) get rich quick
b) get rich slow
c) go broke slow
d) go broke quick
a) Doesn’t happen. These are experts after all.
b) Happens for maybe 25% of the "audience"
c) The remaining 75%
d) Very rare, unless the student applies ridiculously poor money/risk management, but then they would effectively be contravening the teachings we have already accepted as effective.
There are also 4 possible outcomes for the author -
a) Word of this system spreads like wildfire. Book sales decline rapidly.
b) Lots of respect and recommendations, good exemplars for new students to aspire to. More book sales to new students.
c) The usual outcome. More book sales from both new students and the losing students.
d) Criticisms, trolling, negative reviews, suggestions of dishonest dealing with students, maybe even possibilities of litigation. Very rare. No more book sales.
From a reputation and business point of view, outcomes under c) are always best for the expert - sell an effective but degraded and hard to follow trading system: keep selling it and keep selling tweaked versions. Income for life. Happy days.