Research paper · RP26

Best Possible Self, Best Available Evidence

Carrillo and colleagues pooled the best-possible-self exercise in 2019. Across updated randomised and controlled trials, best-possible-self practice produces a small-to-moderate effect on wellbeing (Carrillo d+ = 0.33), optimism (d+ = 0.33; Heekerens g = 0.21) and positive affect (d+ = 0.51; Heekerens g = 0.28); number of sittings is not a confirmed multiplier of that effect. This review asked a narrower question than Carrillo asked. Does one sitting change the effect relative to three or four sittings? Adults who wrote or imagined a best possible future self were compared with any control. Primary outcomes were optimism, positive affect and wellbeing. Searches covered PubMed, PsycINFO, Scopus, Web of Science, Google Scholar, CTRI, ClinicalTrials.gov and OSF preprints from 2001 to 22 September 2026. Carrillo included 29 studies in 26 articles (N = 2,909). Heekerens and Eid later pooled 34 randomised trials (N = 3,675). An update to 2026 added further adult trials that isolate the exercise, including one-sitting laboratory and online tests, four-week writing packages, an app trial and a sittings-randomised anxiety study. Random-effects synthesis of the prior pools, plus sitting-coded narrative of the update, was planned a priori. One sitting reliably lifts same-day positive affect and positive future expectancies. Those mood effects fade within about a week. Three-to-four sittings is Laura King’s original wellbeing protocol. It is associated with wellbeing at weeks, not with a proven larger g than one sitting on the same outcome at the same hour. Writing and imagery are equivalent in the one sitting that tested them head to head. Follow-up effects are small or absent. Certainty is moderate for immediate affect and expectancies, low for trait optimism and later wellbeing, and low for the sittings contrast itself. No adult Indian trial was found. For a workplace programme the honest product is one 15-to-20-minute rep for a same-day lift, and three further reps across a week if the aim is a wellbeing habit rather than a larger first-hour number.