There's a Chinese proverb that covers this well:
I hear and I forget, I see and I remember, I do and I understand.
Mathematicians are self-motivated to do and to understand whereas as students hear and forget then see and remember but seldom do and understand.
Sometimes mathematicians work in isolation but more often they work in collaboration investigating a problem and extending mathematical knowledge into new areas of research.
A fun quote from the 1900's was that there were three great English mathematicians, GH Hardy, JE Littlewood, and Hardy-Littlewood and they, in turn, collaborated with Srinivasa Ramanujan.
https://en.wikipedia.org/wiki/G._H._Hardy
https://en.wikipedia.org/wiki/John_Edensor_Littlewood
https://en.wikipedia.org/wiki/Srinivasa_Ramanujan
In contrast, Ramanujan, for the most part, worked in total isolation using textbooks that were considered second rate. It was only after his papers got to Hardy did he have a chance to collaborate with the Hardy-Littlewood team at Oxford.
Hardy wrote a book called The Mathematicians Apology which is a great read for aspiring mathematicians as is Bell's Men of Mathematics book on the lives of mathematicians which sadly doesn't cover Ramanujan.
https://plus.maths.org/content/node/6725
https://en.wikipedia.org/wiki/Men_of_Mathematics
One last book would be The Man Who Knew Infinity about Ramanujan and his life before and after being a part of the Cambridge mathematical world.
https://en.wikipedia.org/wiki/The_Man_Who_Knew_Infinity