Until I was faced with differential equations I naively thought that every math problem had a clearly stated solution.
I got through it, but math and science lost a bit of their luster to me.
I had already taken all of my calculus and physics in community college and then went on to university. I only needed DE and Statistics to finish all my math requirements for my Civil Degree. It had been 5 years since I had finished my last calculus class. My first semester was DE. I could follow along in class, but at home looking at that those problems, I was absolutely lost.
I even tried to drop the class, but the Professor kept saying I was doing alright. on the 4 tests plus the final I got a B, C, C, D, and a D on the final. He told me afterward that it was my class participation and effort on the homework that kept him from flunking me. I apologized to him for being a complete and utter bonehead.