I am an undergraduate student who is looking forward to work in Theoretical Physics in the future and therefore, I chose a project advisor who is a string theorist. But since, my grades are average and I failed his QFT course (which I am going to repeat anyway), he believes that I may not get a Ph.D position if I continue to do my undergraduate project with him. And he is trying to push me into fields in which I have no interest whatsoever. And he may be right.
I took his QFT course and I worked hard, despite that I failed, not because I am stupid, it is because I am a bit slow and he went with the course at blazing speeds (but I do not blame him, it is not his fault), but since, I took his course, I got motivated and deeply interested to continue with Theoretical Physics. In short, I am in this too deep to discontinue. And he keeps asking me this question,"What will I do if I do not get a Ph.D position in Theoretical Physics ?". And he wants an answer before he continues.
What should I answer him ?