Ezra Pound reports that when Yeats asked Aubrey Beardsley "why he drew horrors", the illustrator replied simply that "beauty is difficult" (Pound, Canto 80). So is clarity. Indeed, there is a sense in which clarity just is the beauty of scholarly writing, its highest stylistic virtue. The best way to achieve it is to say what we mean through a series of assertions, i.e., statements of fact we believe to be true. At one end, therefore, the difficulty lies in the nature of the idea we are trying to express, sometimes in the obscurity of the facts we are going to have to state. At the other end, the difficulty lies in the limitations of language—more precisely, the limits of our mastery of the language. (It can be argued that the expressive resources of the language are limitless.) It is always possible, however, to attain clarity by compromising the idea. Failing to state one fact, we might state another one, a less obscure one. The result may be perfectly clear prose, but we have of course sidestepped the difficulty.
Overcoming the real difficulty of scholarly writing is hard work that requires repeated effort, one statement at a time.
Update at 8:02 AM: I've struck the last sentence because the paragraph seems to me to end more squarely with the previous one. The idea in the last sentence (now struck) actually deserves another paragraph, namely, the one I wrote yesterday.