Concepts or ideas you just can't get your head around?

Was thinking about this the other day. For example, what does a person, deaf from birth, "hear"? I mean they won't hear anything from an external source I suppose, but do they hear anything internally? is there some kind of sensory thing going on inside? a white noise? what is total absence of sound? I suppose without ever hearing a single note they may not have a way to explain what they are sensing in a way that relates to my own experience.

Same goes for blind from birth I suppose. Without any base line, what do they see, if anything. is it all black? all white? all brown? would they be able to explain it in terms we could understand? what does absolutely nothing look like?

For both of these... how do they think? I know I've got an internal monologue running all the time, but I have the benefit of seeing and hearing my own voice so that I can imagine what things could look like or how something might sound.

On the subject of blindness I saw a video about a guy who was going blind. He was losing his vision from the centre, outward. And I initially presumed that what he sees is normal peripheral vision, with a big black hole in the middle. But no. The information just isn't there. The photo cells on his retina are dead, so there is no information. The brain just stitches what is left from each eye together into one image and he showed it as a "jump cut" of sorts, with a discontinuity right down the centre where the left and right obviously don't marry up. So... that begs the question, what happens when the vision failure is complete? what will he see? if what he can't see now just doesn't appear at all, how is that going to manifest in the end? I can't comprehend what "absolutely nothing" will look like for him.

I suppose the classic is space. I can sorta understand it but it is just mind blowing. The amount of stars and galaxies out there, many trillions in just the small patches of sky we've been able to survey. Add on to that the likely existence of trillions more that we can't see because the light hasn't got here yet. And on top of that, the accelerating expansion of the universe meaning some are moving away from us faster than the speed of light (relatively) and thus their light will never reach us!

The actual process or you mean why anyone would find it interesting to sit and do in the first place?

I agree, I think space, as in galaxies etc, is difficult to get your head around but I also think space, as in molecular level, is equally so. At the atomic level, nothing is solid and most of what we see/touch/feel is also just space...just electrons and stuff whizzing around in 'space', all in some sort of organised chaos.

How sounds/music can be recorded on to devices and replayed, particularly vinyl. Doesn’t matter how many videos I watch about it, I will never get it.

People who believe things without good reason (despite mountains of evidence and logic showing the beliefs to be unsupportable).

Quantum mechanics eg double slit experiments showing that single parties go through both slits and interfere with themselves

Relativity

Cosmology - black holes / big bang / expanding universe / how quantum mechanics and gravity can be reconciled

I'll raise you - differentials, kugelmotors

Turkey teeth - Why anybody would want to have a procedure done that effectively destroys your perfectly good teeth and replaces them with stuck on veneers that last 10 years.

Why anybody would think that utterly fake, bright white Love Island/Rylan look is desirable.

Plus from what I understand a lot of the people who have it done have no idea what it involves and end up with destroyed teeth and left in agony.

Trout pouts and those great big spider eye-lashes that young women seem to think look good.

I’ve always been amazed at how tow bars work!

The Pyramids of Egypt. Absolutely blow my mind. We couldn’t recreate those with 100 massive cranes and thousands of workers. Yet they did it way back then with ropes and animal power!