Incomprehensible. Lots of things.
Infinity . . . we can understand the concept, but to actually comprehend it is beyond our mental capacity.
If all the DNA in a human body was laid out end-to-end, it would extend some 34-billion miles. That’s from earth to Pluto and back SIX TIMES. Speeding at one mile per second, to travel that distance would take some 1,122 years. Understandable but incomprehensible.
99.9999999% of matter is just empty space. So, if you were to remove all this space from between the atoms of human beings, you could fit all 7 billion of us into a single sugar cube. It might be true, but my brain tells me it doesn’t make sense.
The number of stars in the universe is something like 3 sextillion (that's 3 with 23 zeros). This is a greater number of stars than there are grains of sand on the Earth. If someone tells me they comprehend that, I’ll tell them I’ve lost faith in their reasoning powers.
The list goes on and on, and begs the question: what do I do with all these incomprehensibles? My counsel would be threefold.
First, don’t lose a wink of sleep over them. Acknowledging that various things are beyond our control (mind control, even) is the first step toward inner peace. The alternative is agony over not being able to comprehend or change or control something. Not pleasant.
Second, keep querying. Curiosity born of exploration is enlivening. It also leads to new discoveries.
Third, glory in a sense of wonder. From the nanoparticles that form the carbon atoms on our insides to the 95% of the universe of which we don’t have a clue, wonder is a wonderful experience. The alternative is dullness, triteness, and complacency. I’ll take incomprehensible wonder any day of the week.