Those moments in life where you are unsure of your place in the world, how to react to it, or what to process within it. They never fail to happen when it would no doubt be best that they didn't.

The first day of school/work/anything new.
At a party when being social is what will make it fun.
The moment when you need to be poised and confident.

In my experience, only someone who knows me very well will notice that I'm having one of these moments, but they plague me for weeks, months, sometimes years... "Well, if I'd just said....... maybe this would've happened..."