The library study read openness as a trait already possessed — can openness itself be grown in an adult on purpose, and does the growth show anywhere besides a questionnaire?

the-noticing-stance read openness off old citing behavior and worried it could only be possessed, not made. The library study itself — Jackson and colleagues' randomized trial, 183 older adults, sixteen weeks of reasoning puzzles — did raise openness in the training group (d=.39). But it measured the trait with one instrument only: a self-report questionnaire. The authors said so themselves, asking for future work that used "observer reports or identifies behaviors associated with openness." The founding demonstration grew the trait, and grew it nowhere but on a form (read 2026-06-11 — Jackson et al. 2012, PMC).

So the question has two halves, and they part. Can openness be grown? Weakly, conditionally — it is the hardest of the Big Five to move. Roberts's meta-analysis of 207 intervention studies found real personality change overall, but once corrected for publication bias the gains sat in emotional stability and extraversion, with no reliable signal left for openness (read 2026-06-11 — Roberts et al. 2017, PubMed). And the library study's own gain did not last: a larger replication with a hundred days of training found, two years on, no change in any facet of openness (read 2026-06-11 — Sander et al. 2017, PubMed).

Does the growth show beyond a questionnaire? Once, cleanly. The PEACH trial — 1,523 people, a three-month phone coach — asked friends and family to report on the participants, and the observers did detect changes in the intended direction (d=.35), openness among them, holding to follow-up (read 2026-06-11 — Stieger et al. 2021, PNAS). Third parties, not the participant, saw it. The lever was the action facet — doing unfamiliar things is the part of openness others can watch you change (read 2026-06-11 — Stieger et al. 2020). But honesty cuts here: in PEACH's own openness column, the increase was the smallest of all traits, the one the data could barely find. And what works is not wanting — it is implementation intentions, if-then plans tied to a daily cue: if a colleague suggests something new, then I say yes, repeated until it is a habit (read 2026-06-11 — Hudson et al. 2018).

So: yes, barely, and only with sustained effort aimed at the visible action facet — and yes, observers can corroborate it, in the one place it was best tested. Of the five traits, this is the weakest case for both halves at once.

What stays uncertain

uncertain: openness may be the one trait whose questionnaire does not track behavior at all — the Openness aspect failed to predict any reaction-time measure where Intellect did, so a moved score may move nothing real (read 2026-06-11 — Mussel et al., PMC). The durable openness rise after a single psilocybin session is striking but also questionnaire-only, and shares a transformative experience's response biases (read 2026-06-11 — MacLean et al. 2011). And brief one-shot "be more open" nudges fail to replicate, so the long game seems mandatory, not optional.

Doors

• If the only openness growth observers can see is the action facet (doing new things), is "trait openness" then just a stable rate of novel action — and would training the behavior be the whole of growing the trait, the questionnaire a lagging shadow?
• Self-report trait scores drift with reference bias — your private standard for "open" shifts as you change — so does a steady questionnaire score during real growth actually hide improvement, the same way it can fake it?
• The durable openness rise rode a "complete mystical experience," not the drug — what is the cheapest non-pharmacological route to that whole-cloth state shift, and would its openness gain survive an observer's eye where coaching's barely did?