Secret of Success - I Do Not Know

How does these words " I do not know" relate to secret of success?

• It infers opportunity.
• It infers a chance to learn things.
• It gives the flexibility.
• It gives one the cushion.
• It eases pressure.

When you donot know something, others donot expect from you. When there are no expectations, naturally no pressures involved. [But here the mindset should be set I must learn or I must get to know and then achieve success.] Generally people consider saying the words "i do not know" as a great mistake. Rather they end up giving some answers not minding whether it is right or wrong. When they do so, they are spoiling their reputation.
Do you get my point? They are killing the trust on them. Then how can they expect success?

Image courtesy: carrotsandcompany.com