This is so true: I remember in high school studying calculus from a random book which made me think that calculus was about was a bunch of tricks for doing integration and differentiation. A few years later when I first start working through Spivak's excellent book on Calculus, It was one of the hardest things I had ever done but the sheer magnificent beauty of the structure on which most of modern calculus is built on and how it gradually evolved comes to light. It is really both a journey in history and time and building mental models that reoccur through so many branches of mathematics.