Op's article suggests that there's only "brain exercise" when it's difficult to the point one feels bad or even painful. Very different from "simple joy" as you

Op's article suggests that there's only "brain exercise" when it's difficult to the point one feels bad or even painful. Very different from "simple joy" as you describe. I'm not saying that there are studies supporting that (I'm not sure), but there's a clear difference we should be aware of before discarding the idea.