not being able to guess, afraid to come up with a hunch, not willing to use a ballpark guesstimate, afraid to give a viewpoint in case it's not the perfect one, being uncomfortable with tentativeness.
A: How far is it to LA do you think?
B: I have no idea.
A: But what would you say?
B: I haven't a clue.
A: Would it be one mile?
B. I wouldn't know.
A: How about 20 light years.
B. Gee, there's no way of even imagining how far it is.