I've had editors over the years who couldn't find a clue if it was stapled to their butt.
I think what's really hard is making sense and making what you write clear and smooth-flowing.
In general, what is written must be easy to read and easy to speak; which is the same.
There are people who believe in an absolutely transparent prose; with every respect for clarity of expression, I don't.
it is all very well for you to write simply and the simpler the better. But do not start to think so damned simply. Know how complicated it is and then state it simply.
And how is clarity to be achieved? Mainly by taking trouble and by writing to serve people rather than to impress them.
I write as straight as I can, just as I walk as straight as I can, because that is the best way to get there.