What does “I don’t know” cost?

For each of 5271 graded answers, the analysis recorded how the investor reacted. After a plain “I don’t know”, they pushed back or challenged the founder 21% of the time. After an answer that dodged the question, 17%. After a direct answer with a fact or a number, only 7%.

Vague answers drew fewer challenges (9%), but not because they worked: investors often just moved on to the next question. Only 29 answers were an open “I don’t know”, so read that bar with care.

Not knowing is not fatal, but leaving it there is. Say what you do know, give the closest figure you have and say when you will have the rest.