The cliff looks deeper from the edge than from halfway down. Starting is the scariest height.

Fear peaks before the first move, not during it. Standing at the edge you are imagining the whole descent at once, with no information and nothing to do with your hands. A few metres in, the task becomes specific: this hold, then the next one, and the specific is always less frightening than the total.

So make the first move smaller rather than braver. Open the document. Send the one line message. Put the shoes on. You are not trying to summon courage for the whole thing, because that courage does not exist at the edge. It shows up once you are on the wall.