WHY are you interested in "(research interest)"?

[FlyingGoldFish]

Hi everyone,

I am having some hair-pulling time trying to answer the question in the title. I have already learned that statement of purpose and/or personal statements are serious deals that explains your goal, research interests, and your distinct fit for the program. I do have few branches of research interests that I narrowed down, which I can envision doing for the rest of my research career. However, I have a very hard time explaining WHY I want to do it. Most of the articles and tips that I read from books/forum tell you to explain why I want to do that particular research. The problem is that I don't have a eureka moment that decided my research interest. Even if I do, I am afraid to use personal story examples that derived my commitment to particular research because of possibility of being overlooked. At the same time, I can't just write, "I want to go into this field because I like it, I've done it, and I fit well in it." It won't make me stand out as a serious candidate, right? Do I need to do more and more thinking? Am I on the right path and just answered my own question?