Action/dx = d/dt(dLagrangian/dv)-dLagrangian/dx = 0: “The Theoretical Minimum - What You Need to Know to Start Doing Physics” by Leonard Susskind, George Hrabovsky
Math is just a skill, like any other and not everyone can do it. What gets my goat is the "anyone can do anything if only they try hard enough "attitude. No, they can't. Some people are good at certain skills and not other, and others have different skills. I happen to be good at math. I get annoyed when people say "Ooh, you must be so clever!" when I tell them. No - I just have that particular skill - I can no doubt be as dumb as the next person at something else. As Courtney Barnett puts it: "The ambulance driver thinks I'm clever 'cos I play guitar /I think she's clever 'cos she stops people dying." Laughing at general illiteracy isn't so funny, because that is a relatively simple skill that most of us can learn, and it hurts people not to have it; but Quantum Mechanics? Come on, no one groks it, and it really doesn't matter for most of us.
If you're into Learning Physics, read on.