The three most courageous words to say in the English language are "I don't know."
In our wiki-based, google-centric, know-it-all culture, being able to admit that you don't know something is not only brave, it shows strength of character and confidence. To say "I don't know" in our culture is to admit some sort of fault, some sort of stupidity. It's inane. If someone is an "expert" or "professional" in something and they respond "I don't know," to a particular question, they are considered weak. This is not the case.
When my daughter was little and she'd ask the "why is the sky blue" questions, if I didn't know the answer, I'd say "I don't know, but let's look it up when we get home." And we would, and we would learn something. The most important thing that she learned was that it wasn't as important to know something off-the-bat as it is to know how to find something out. That is the critical skill.
But even more importantly, it's important to be able to admit when we don't know how we're feeling or what we think on a certain topic. So many people go off half cocked speaking before they think about topics they've given no real consideration to. And they do this just to sound as though they "know" something. When really they don't. I've had multiple multiple conversations with friends and loved ones about topics to which I've responded, "I don't know what I think about that." Albeit, it usually only takes me a few moments to deduce what I think about the topic, but when I initially don't know, I say so. Why? Because it's important to me to model the behavior that not knowing is ok and even preferable, if it's the case, to nattering on about something.
I wish politicians were allowed to say that they don't know the answer to something when they haven't studied it thoroughly. I wish they weren't thought of us unprepared or stupid for saying "I don't know yet what I'm going to do about so-n-so, let me get back to you." An answer like that would be the opposite of stupid. And yet, time after time, politicians who even SEEM to be 'making it up on the go' are seen as stupid - when really, they're just giving the people what they demand, an "answer." It's too bad.
The best teachers I've ever had have been able to say "I don't know." And then help us all find out the answer. It's been relieving to know that in order to be smart, you don't have to memorize the entire encyclopedia of humanity. Forgot a date? Look it up. Don't know the name of a battle? Look it up. Can't answer a math problem? Solve it. The idea that working on a problem to solve it can't be part of what makes us smart is a huge error in our educational system and in our thinking in this culture.
As for me, I'm going to keep on admitting when I don't know something until I do know it. That's the way to keep me honest.