I don't think we really disagree here. Yes, you need to be smart and realistic about your capabilities. My Feynman et al. example wasn't advice for students, it was a refutation of the idea that theses aren't particularly important or indicative of future success (which is what you imply with the Einstein example).
Edit: "OP" --> "you". Sorry, I didn't realize I was talking with the author. Thanks for the thoughtful reply!