I know nothing about physics - I took a class in high school, and that's it - but there are a couple of explanations: 1) These are old lecture and the whole pa

I know nothing about physics - I took a class in high school, and that's it - but there are a couple of explanations: 1) These are old lecture and the whole particle/wave thing, while known, was just thought of differently back in the 1960's. 2) My guess - he's making a generalization to set up for a "blow your mind" moment later in the lecture series. I know nothing about (1), but I do (2) all the time when I teach. One of the things I do is that I try to simplify the building blocks of whatever I teach early on. I simplify things and I repeat them both verbally and visually, doing everything I can to drill my students with these facts. Then, later in the class, I show the exception cases. This does two things: 1) it gets their attention and 2) it reminds them of the general rule. I love doing this because you can immediately see comprehension in students' faces and it re-establishes my control over the classroom. (Anyone who's taught knows that a dialogue in a lecture room is doomed to failure; you're the teacher - you're in charge.) My guess - again, I know nothing about physics and nothing about Feynman - is that he's making a tactical decision in how he presents material to maximize student learning over the totality of the lecture course.