the observable universe
Just when you think you have a vague handle on how it all works, someone comes along and says, wait a minute, the universe is actually expanding at an ever increasing speed.
This kind of throws a spanner in the works of the previous models of how it all came into being and what might happen in the future, as it implies there are completely unknown forces at work in the universe. (no surprises there)
I like those spanners, what a relief to realise we are not close to knowing everything.
Humility returns. I always find it amusing to hear various scientists say they think we are on the verge of the 'ultimate theory of everything'. Perhaps their heads are in a process of ever increasing expansion also.