A small piece of reliable information can bring more comfort than a large promise built on hope.

Reassurance that is not grounded gives nothing to hold. Telling someone it will all be fine asks them to believe a thing you cannot know, and it often has the opposite effect, because the gap between the words and the situation is obvious to them. One true, small fact, the appointment is on Thursday, the results take a week, someone will call, gives the mind somewhere to rest. Certainty about something small beats optimism about everything.

When you want to comfort someone, find one accurate thing you can actually tell them. Say that, and stay rather than filling the silence with promises.