The science

The science behind the book.

Every key claim in this book came out of more than a thousand hours of one-on-one work. And every one of them has research behind it.

Chapter 6

“The fight is the problem, not the solution”

Original experiment

Wegner et al. (1987)

The original “white bear” experiment: trying to suppress a thought paradoxically produces the very obsession or preoccupation it is aimed against.

PubMed →
Meta-analysis

Abramowitz, Tolin & Street (2001)

Meta-analysis of thought-suppression effect sizes in Clinical Psychology Review: a small-to-moderate rebound effect, confirmed, varying with the nature of the target thought.

ScienceDirect →
Direct application

Rassin et al. (2003)

After attempting to suppress anxious thoughts, participants experienced a rise in anxiety and in thought frequency. Suppressing anxious thoughts can paradoxically increase anxiety and cause or maintain anxiety problems.

PubMed →
Chapter 5

“Secondary gains”

Systematic review

Fishbain et al. (1995)

A review of 166 references in The Clinical Journal of Pain, including 24 secondary-gain studies and 14 reinforcement studies. Conclusion: the results support the potential importance of the secondary-gain concept for understanding illness behavior.

PubMed →
Clinical study

Dutch psychiatric study

Of 166 patients, 70 (42.2%) reported expecting secondary gain while in treatment, and that expectation was significantly linked to worse outcomes. In only 9 of 147 cases (6%) did patients explicitly voice those expectations to their psychiatrist.

ScienceDirect →
Chapters 6, 7, 9

“Acceptance, not control”

Meta-analysis, 39 RCTs

A-Tjak et al. (2015)

ACT outperformed control conditions (Hedges' g = 0.57) and was superior to waitlist (g = 0.82), psychological placebo (g = 0.51), and treatment as usual (g = 0.64). Published in Psychotherapy and Psychosomatics.

PubMed →
27 RCTs

Yu et al. (2025)

2,860 participants: ACT did not outperform CBT, but was significantly more effective than other active controls. Gains in psychological flexibility significantly predicted reductions in depression and anxiety.

PubMed →
Review of 20 meta-analyses

Gloster et al. (2020)

The key point: from the very beginning, ACT's authors held that its goal is not the reduction of inner states — although that may happen — but the promotion of functioning and well-being.

ScienceDirect →
Chapters 1, 4

“The body remembers” / Adaptation

Original paper

Van der Kolk (1994)

In Harvard Review of Psychiatry: trauma is stored in somatic memory and expressed as changes in the biological stress response. Intense emotion at the moment of trauma sets up long-term conditioned responses to reminders.

PubMed →
Implicit memory

Van der Kolk (1998)

Traumatized people can “know” the emotional valence of a stimulus and be aware of related perceptions, without being able to articulate why they feel or act a certain way. Janet proposed that traumatic memories are split off from awareness and stored as sensory perceptions.

Wiley Online Library →
Chapter 10

“A second is enough”

Umbrella review, 415 trials

Schleider et al. (2025)

24 systematic reviews covering 415 unique trials in Annual Review of Clinical Psychology: 83.33% of reviews reported significant positive effects of single-session interventions for anxiety, depression, eating problems, and substance use. Effect size = −0.25.

Annual Reviews →
12-month follow-up

Hoyt et al. (1992); Bloom (1997)

58.6% of clients reported that a single session had been enough, at 12-month follow-up. Bloom's meta-analysis found one intervention can be as effective as long-term psychotherapy. More recent research: 50–70% of clients show improvement after one or two sessions.

Single Session Therapies →
Chapter 9

“Love, not technique”

Classic breakdown

Lambert; Wampold

Lambert estimated that 15% of outcome variance comes from specific techniques and 30% from common factors. Wampold concluded that therapeutic factors together explain 13% of outcome variance, with the therapeutic alliance identified as the most effective component.

Meta-analysis, 295 studies

Flückiger, Del Re, Wampold & Horvath (2018)

A correlation of r = 0.28 between therapeutic alliance and outcome, stable across studies. Consistent regardless of therapy type.

ScienceDirect →
Contextual model

Wampold (2001/2015)

Meta-analytic and hierarchical modeling showed that common factors explain a far larger share of outcome variance than specific techniques. Specific techniques did not explain a clinically meaningful share of variance.

Chapter 15

“Understanding has an expiry date”

Meta-analysis

Jennissen et al. (2018)

The first meta-analysis of its kind in the American Journal of Psychiatry: over 12,000 abstracts screened, 261 full papers assessed, 22 studies included. Insight is considered one of the most important mechanisms of change — but the size of its correlation with outcome is comparable to the therapeutic alliance. Moderate, not magic.

AJP →
Key finding

Intellectual vs. emotional insight

Intellectual insight is not enough for behavior change. Change happens mostly through emotional insight: understanding accompanied by emotional experience. Intellectual insight only prepares a person for the experience of emotional insight.

These studies test the mechanisms the book describes. They do not test this book, and they are not a promise about any individual outcome. Source links point to the journals' platforms.

The book turns this research into one evening of reading.

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