Barbara and Tracy discuss assumptions, facts and creative problem solving. 

They underline the importance of exposing and challenging assumptions in order to understand wicked, or complex  problems.

Reference is made to the ladder of inference proposed by Chris Argyris, and you can read more about this here.

Peter Senge proposed the left hand column exercise in his Fifth Disciplinary fieldbook.

You can find more about Barbara at barbara-wilson.com, and Tracy at tjstanley.com.