This practice is most credible when the team can point to a recent incident where a mistake was surfaced early and handled without blame.
The surrounding process should make it easy to report ambiguity, not just defects. That keeps the card focused on the social system that allows technical issues to be spoken about.
Psychological safety is not softness. It is a control mechanism for surfacing weak signals before they become outages, handoff failures, or silent workarounds.