What is hardest to comprehend
Big bang (Nothing existed before, not even time) <--- this one.
The observation we've made, and still maintained, is that the universe is moving / expanding.
So, we've theorized that it was all in one mass or one atom at some point and something hit it and everything fell out; minerals, gravity, time, higher/lower dimensions, etc.
Now, it is suggested, the universe was as is (minerals, gravity, time, higher/lower dimensions), but something kicked it into it's expansive direction - the Big Bang.
So, the Big Bang theory isn't going away.
"A new paper in Physical Letters B has the popular press wondering if there was no Big Bang, but the actual paper claims no such thing... The Big Bang is a robust scientific theory that isn't going away, and this new paper does nothing to question its legitimacy."
But, the idea that everything in the universe came from one piece of matter (or some singular focal point) has become more so as something that is hard to comprehend and prove.
The universe always existing and will continue to exist is still no easy thing to comprehend, but it makes much more sense than thinking we came from one sole piece of something as a result of the Big Bang.