What Lincoln lacked in preparation and guidance, he made up
for with his daunting concentration, phenomenal memory, acute
reasoning faculties, and interpretative penetration.  Though untutored
in the sciences and the classics, he was able to read and reread his
books until he understood them fully.  "Get the books, and read
and study them," he told a law student seeking advice in 1855.
It did not matter, he continued, whether the reading be done in a small
town or a large city, by oneself or in the company of others.
"The books, and your capacity for understanding them, are just
the same in all places.  . . .  Always bear in mind that your own
resolution to success, is more important than any other one thing."

Doris Kearns Goodwin, Team of Rivals: The Political Genius of Abraham Lincoln.
New York: Simon & Schuster, 2005, p. 54.