Not that I think there are invisible pink unicorns in the room with me, with you and with everyone, but are you sure they aren't?
I mean maybe there are invisible pink unicorns standing besides all of us? How would we know?
Probably best to conduct myself as though there are invisible pink unicorns all around us, since I can't be sure there are not any.
Then there's the leprechaun problem to consider, and especially weather or not the possible leprechauns and invisible pink unicorns get along with each other.
As if that's not already complicated enough, someone suggested that there might be giant dinosaurs outside. Since I haven't looked outside for at least 5 seconds I can't be sure if there are or aren't, so now I need to keep that in mind since I can't really know.
It's hard living in a world where I have to consider extraordinarily implausible things as though they are as probable as my own existence.