Here's how I know I'm wasting my time.
I don't think I've get to submit a single assignment, or piece of work (except for the occasional comment in class or answer on a test, which are scarcely considered in the scheme of evaluation) of which I've ever felt proud.
I think this is basically how one figures out that they're in the wrong field. I don't feel good about the work that I do. I don't feel good about myself when I do it. I just don't do this well.
I take no pride in my work. I think that's how I know that I'm doing the wrong work.