I studied calculus on my own in my twenties, and I think the textbooks' focus on rigor led me down a lot of blind alleys before I started trying to come to an i

I studied calculus on my own in my twenties, and I think the textbooks' focus on rigor led me down a lot of blind alleys before I started trying to come to an intuitive, often graphical, understanding of the problem before attacking the rigorous view. (There is a good textbook from 1977 that was reprinted by Dover in 1998, Morris Kline's "Calculus: An Intuitive and Physical Approach", that I wish I had available when I was studying.)