What keeps them awake at night, indigestion boiling up their esophagus, eyes open, staring at the ceiling?
What are they afraid of?
What are they angry about? Who are they angry at?
What are their top three daily frustrations?
What trends are occurring and will occur in their businesses or lives?
What do they secretly, ardently desire most?
Is there a built-in bias to the way they make decisions? (Example: engineers = exceptionally analytical)
Do they have their own language?
Who else is selling something similar to their product, and how?
Who else has tried selling them something similar, and how has that effort failed?