Sometimes people say they don’t believe in things to means that they don’t agree with or subscribe to a concept. Someone might say, "I don’t believe in tax cuts for the wealthy." I always think for half a second, "do you not believe that they are good or do not believe they exist." It’s entertaining to imagine not believing in common things that we take for granted.
If you think about it, such skepticism is is not always totally unjustified. I’ve heard of people that don’t believe in plate tectonics which, if you think about it, is not a totally insensible thing to not believe in (although I do believe in plate tectonics myself).
I think it would be a good experiment if everyone would, for one day, act as if they don’t believe in things that they have not personally seen or experienced convincing evidence of existence.
We should all spend one day in a world without big things, small things, or concepts; no germs, macroeconomics, political assassinations, and much more.
The next day we will return back to normal but I think we will all have a lot more perspective.