What is witnessing stance?

According to the book Essential Elements for Effectiveness (4 Edition) Published on 2009: The Witnessing Stance is the ability to stand apart from ourselves to view ourselves from the outside. The ability to have the choice to be a witness to your own life.

You cannot always change situations (i.e. external stressors or events) you are faced with, but you can always change your reaction towards the stressor. Assuming the witnessing stance allows you to do this.