A First Course in Differential Equations for Scientists and Engineers
I took DiffEq as an EE undergrad and, to my surprise, aced the course. For some reason, the concepts just resonated with me unlike other math courses where I had to work to gain an understanding of the material. A few years later, after graduating, I was taking courses leading to an MSEE and Partial DiffEq was offered as an option that I took. Thinking it was going to be similar to regular DE, I was soon in way over my head. Totally different material and concepts. I did end up passing the course but I can honestly state that I don't think I deserved it.