Fed up with being on the hook for a three-digit bill one too many times, I recently bought a book on car maintenance hoping to learn simple repairs by myself. The mechanic on the cover looked like a trustworthy figure; his long gray beard attested to decades of experience. When the book arrived the next day I immediately removed the foil and read the preface, copied below in its entirety:
You fool. You rube. Nobody has ever become a car mechanic by studying a book; true gearheads can trace their lineage back to Henry Ford and have motor oil coursing through their veins. And if you don't, you'll never so much as replace a spark plug, ever. Live with it. In lieu of practical advice, the rest of this book is filled with pictures of the author's most recent family vacation to Fiji.
Needless to say, I did not actually buy a book like this. I'm proving a point by putting the fundamental problem in front of a funhouse mirror. Self-help books exist for the reader to become better at something, be it car repairs, processing emotional hurt, whatever. If your overarching conclusion is 'all is futile; the die was cast nine months before your birth,' you have utterly failed to fulfill that singular purpose. Quite simply put, you don't have a book.
Another thing about self-help books. The author is essentially a teacher to an audience of one. As such it is expected you possess a certain expertise*, and precludes a belief reading the book does nothing to make the reader better at some skill. If I genuinely believe car mechanics are born, not raised, would I ever write a book on car maintenance? Would you?
Two strategies exist to alter both tone and message of your book. One for the bread writer, the other for the brain writer.
Brain writers are students as much as they are teachers, and possess a strong academic spine. Their work might be popular and earn big royalty paychecks, but they primarily write for the love of sharing their skills, insight, and the love of teaching itself. Re-examine your research. Apply basic scientific literacy. Did you fall for common biases? Spot any confounding factors? Make flawed assumptions? Read and reread your work. Have someone else critique you. After all of this, determine if your expert opinion has changed. If it has, rewrite where necessary. If not, don't publish.
The bread writer's main concern is earning a paycheck. If you are one, simply delete the offending chapter and replace it with the mushiest pablum in your pantry.
* You'd be surprised how many bread writers exist.