Informatively, how discombobulating it can be to know something for sure and yet, simultaneously, be aware that you don't know at all. I think of this in terms of spiritual endeavor, but today, a story out of Wisconsin put new meat on the bone.
In Clintonville, Wisconsin, unexplained booms have disrupted sleep patterns and assumptions. It's not earthquakes. It's not mining. It's not military exercises. And it's not a bunch of other speculative searches for the cause ... including aliens. But people in Clintonville know a boom when they hear it and they've been hearing it for at least three nights running.
Concrete evidence with no clue as to what that evidence is evidence of.
That'll upset your apple cart.