My guess would be that the left ones are old and difficult to read books professors like precisely because of that, and the right are books which explain things in a more understandable way. But that’s just a guess based on that that’s exactly how I, as a former physics major, would use this meme for physics books.

No, your math is wrong. The chance you’re on the main track is actually twice as high. Imagine it like this: When all numbers 1-6 would come up once, there have been 10 people overall on the main track and only 5 people on the side track