Others too.

First because "Effective communication requires effort" from BOTH sides.

And also because others can deliberately misinterpret your words for their own gain, or because they're biased, or because they've been primed by factors outside your control, or for lots of other reasons...

>If someone is unable to clearly express themselves without being misunderstood

That has been the case for everybody for the entirety of history.

There are better or worse ways to express something, but there's no foolproof way to express even the simplest thing in a way that you "wont be misunderstood".

Sometimes even saying "yes" or "no" with the wrong tone (or what the other person perceives as the wrong tone) can be misunderstood.