True story: when I was fifteen, I went on a school field trip to the Smithsonian Air and Space Museum and picked up a copy of BMW in the museum bookstore. I was determined that I was going to make it out of my podunk little town and become an aerospace engineer, so I decided to work through the book on my own.

The problem was that I had never had calculus, much less differential equations. I fact I didn't know what calculus was; I only knew it as a word that meant "really hard math". So I made it about five pages in and realized that I had no chance. BMW stayed on my bookshelf.

Ten years later, I was in a graduate program for aerospace engineering and had finally made it through all the pre-recs for 600-level astrodynamics. BMW was one of the textbooks for the course. The moment, a month into that class, when I opened the book and it actually made sense was one of the highlights of my life, and that copy of the book I bought as a teenager is one of my most prized possessions.