"I don't know." Some people seem to have real difficulty speaking those words. There are so many things most of us don't know that these should be easy words to speak, and we should speak them often. Instead, we tend to treat them as a confession or an apology. We might add a "Sorry but..." in front of them. An astute listener might hear the volume of our voice dip a bit when we say them, almost as if we are afraid others might hear. Maybe we're going about this all wrong. Maybe we should applaud people who are willing to say "I don't know." After all, they are being honest.
I'd guess that part of the reluctance to say "I don't know" comes from our unrealistic expectations of ourselves. We want to be knowledgeable. I think most of us know that nobody knows everything, but this sometimes seems what we expect of ourselves. But we don't know everything, and we should accept this as inevitable. We should also recognize that we are in good company. Nobody else knows everything either.
Some of our reluctance probably has to do with our concern about how we are perceived by others. It is not just that we want to be knowledgeable; we want to be perceived as knowledgeable by others. And even if we know that we won't always be perceived as knowledgeable, we at least don't want to be perceived as ignorant or stupid. This often leads us to hide our uncertainty or even to pretend to know things we don't know. This probably does more harm than good to our reputations. Nobody likes a know-it-all. And don't you remember as a child how refreshing it was when one of your parents admitted they did not know something? You did not lose confidence in them; you felt closer to them. You found something else you had in common!
I think there is a vast difference between not knowing something and what we might call ignorance or stupidity. Acknowledging that one does not know something and then seeking to learn more to improve one's knowledge is about as far from ignorance or stupidity as one can get. When we refer to someone as ignorant, we are usually saying that they are intellectually incurious. The problem is not that they do not know something; the problem is that they either don't know they don't know or don't care enough to do anything about it. When we refer to someone as stupid, we start there but then add our dislike for the person.
I've always found not knowing to be a great motivator. If I was convinced I knew everything worth knowing, I don't think I'd be able to drag myself out of bed in the morning. It is hard to imagine I'd have any reason to go on living. Not knowing drives me to learn, and it is that drive that keeps me going. And so, I'll wear "I don't know" as a badge of honor. I don't know, and that's why I am trying to learn something every day.