“Humans like to think that they got to Here and Now through a clear journey of decisions made correctly. Alternative choices and missteps are lost to the unconscious.
Asking people about their journeys and even observing their journeys can get stuck in the idea that the unitary path is obvious and unique.”

This is a good example of the constant tension between the feelings of 'we need more information before we start' and 'let's just start and we'll learn as we go'.

Sommerville's point is good, but we need to remember: the fact that the User Journey is not the single obvious path does not mean that we need to create more Journeys to try and create a complete picture.

It means we need to bear in mind that our information is imperfect.