I didn't know but I do now I have watched this:

 

We old guys have known this since birth.
https://forum.allaboutcircuits.com/threads/digital-coax-cable.87828/post-632975

Another interesting question is why the free-space impedance of the universe is ~377Ω.

https://www.testandmeasurementtips.com/the-characteristic-impedance-of-the-universe/

 

Well, for me, since I was 18. We derived the the characteristic impedance equation in my first college physics course (electricity and magnetism, I placed out of two semesters of mechanics)