Writers must write clearly, as well as the good thinking part. When I sub something to my online writing group, one of the comments that often comes back is that 'such and such is not clear to the reader.'
I see the comment on the subs of other members of the group, too. Why in the world do we write something that confuses the reader rather than lets them know exactly what the situation was or what a character did? It's not a deliberate action.
One reason is that we are oblivious to what we've done. In our mind, as we write, we see the scene with total clarity. We know where it is, who said what, the placement of this or that, the motivation of a character. We see it because we created it. It's especially true when writing memoir or creative non-fiction or family stories. There was an old tv show called You Are There! Sometimes, writers are there all alone; the reader is not and they are depending on the writer to put them there.
If you are not already checking your work for clarity when you proofread, add it to your checklist. It's very important that we write so that the reader sees and understands what is going on or who is saying what. Sometimes, it's crucial.
One way to be able to catch this problem is to let your piece of writing sit quietly all alone for several days after you finish writing. Go on to some new project and come back to this one later. The problem is more likely to show itself then.
Having someone else read your work is always helpful. These readers will catch myriad errors that your own eyes have passed over. I see the errors in other writers' work much faster than when proofreading my own work. It's just the way it is. And that is one good reason to either belong to a critique group or have a writing buddy who will read your work.