I began drafting this post before the disappearance of flight MH370. And that gives not knowing a terrible meaning.
I had planned to remind you what it was like being six, and the teacher asked you something and you thought and thought and knew you should know the answer but somehow you just didn't, so you made it up. At the time it made more sense to get the answer wrong than admit you didn't know.
Too often it feels as of no one has grown up.
When politicians make it up it goes something like this: I can't tell you that right now, but what I can tell you is ...
Newspapers do it differently: eat less butter, eat more butter; working mothers help children be more independent, working mothers impede the development of healthy attachments in small children ... They take a research study, read the conclusions, precis that - because the alternative is suggesting that there is conflicting evidence.
There are cultures in which saying 'I don't know' is shameful - if you are lost and ask the way, it's best to ask three people and go with the majority as it's likely that someone will have made up the directions.
But not knowing - everyday not-knowing - is the cornerstone of curiosity. And without curiosity how can we learn? Without curiosity there are no new ideas. Without curiosity we stagnate.
But not knowing can be uncomfortable. It reminds of us teachers, of everyone looking at us, of not-knowing being the equivalent of ignorance.
I still think that not-knowing is often an opportunity, and that being honest about it is challenging, and can be fun. It can send us rushing to our bookshelves, or to Google.
But then the terrible not-knowing for the friends and family of those on board flight MH370 - their not-knowing is more painful than breathing.