There are still other dangers. Mind-altering substances make several appearances and do, in fact, alter minds. Kubrick has taken his characters to that emotional edge, ripped off a bit of the surface, covered it up again, ripped a little more off, etc. Now the consummate professional knows that the risk was not worth it, but he's not sure what his losses are. All he knows is that he has to cut them.
Courage is grace under pressure.
He's under a lot of pressure. So is she. She got them started on their trip out to the edge. Now she has to find their way back. She does it with the very last word.