Watch for the moment a what if turns into a when. That small slide, from a possibility into something you can already picture in detail, is where worry does most of its damage.

What the research says

Within a cognitive behavioural treatment programme, reductions in how badly people tolerated uncertainty accounted for the reductions in their worry, which points at the not knowing rather than the content of any particular worry as the thing to work on. That was a mediation analysis inside a trial, so the direction is inferred rather than proven. It fits what people notice anyway: settle one what if and another one arrives.

Strength of evidence: one line of research. A single study, or a theoretical account.