Say I wish to pursue a phd in some CS related field. How knowledgable do I have to be in the field I am pursuing? I'm asking because some things happened recently that led me to doubt myself:
I have been doing some machine learning research for the past year and I'm working towards a first author conference submission (as an undergrad). As I was drafting my paper, my professor asked some questions about the project I'd done - such as why I chose certain methods over others, or why I choose a particular parameter for my experiments and more. And I realised that I couldn't answer them. See, in my project, I didn't create anything new. I simply took existing methods and applied them to a relatively unexplored research area, which means that I was just following what other people did. To take something and apply it somewhere else doesn't really require that much knowledge in my opinion. I've been reading papers, trying to explain why some methods outperform others and often times I do not fully understand them. The high level logic maybe I understand, but certainly not the in-depth algorithms or implementations.
I feel as if I know nothing about this field (and I probably really don't know much). Yet, my professor offered me a phd position. I feel like he was placing too much confidence in me. Have I managed to fluff my way through this project, or is this something that happens to other people too? Especially those who completed their bachelors and went for a direct phd.