From 38:27 to 39:20 Professor Susskind talks about how it's not so obvious that the superposition of forces works. Why is it not obvious though? Isn't it an inevitable mathematical consequence of vector addition? Have I misunderstood the superposition principle? Professor Walter Lewin from MIT also said something similar once. "Is it obvious that the superposition principle works? No. Do we believe in it? Yes. Why do we believe in it? Because it is consistent with all our experiments."