I took two courses in ODE. I got an A in the first semester. I still have no idea what they are or what's going on. It's all just relationships and patterns to me--but with no intuition or understanding behind them. It never "sunk" in like Calculus did where "Area under the curve" and "tangent line" are super obvious in retrospect and immediately applicable to your daily life. "What's velocity? The change in distance over a unit of time." Done. Presto.