Could it be, that a person can be boring, even though they do things? Is it the lack of the ability to express oneself? Lack of focus? [I'd Rather Get To Know You Than Small Talk]

I don't think there's a universal pattern to describe boring. Different people think and feel different things. I don't think that self expression or lack of focus are exactly the particular traits that contribute to being boring. I think it's preference of the other; because preference is different for everyone