I'm not sure.

It's actually easy to say, "I'm sure this is going to happen".

The truth is that we are never sure.

It's just that it takes a lot of emotional labour to see the alternatives, to see how the thing we are sure about is still uncertain.

We are afraid of being uncertain or atleast of acknowledging that we are.

"I'm not sure" or "I think there is a 30% chance this will happen" doesn't make us less confident, instead it gives us an opportunity to see things that we are not able to see yet.