The fool doth think he is wise, but the wise man knows himself to be a fool.

We, the humans are all born with some kind of instincts, later on in life we gain knowledge, common sense, experience etc and yet, we still die ignorants. It is a shame to scream your wisdom to the world, that is what fools usually do. Wisdom is unlimited, and we only possess some very small portion of it. Saying, i do not know, is your first step towards wisdom.