I don't disagree speech is hard, but _everything_ gets messed up when you are tired or recovering, e.g. eye hand coordination. It's just that its easier to spot it when speech is less than perfect, then when coordination is less than perfect.
I agree that a lot of things are messed up when you are tired or recovering but after brain surgery she was in perfect condition except functions located it the region of the brain that was operated on and her speech. After all the youtube videos I watched to prepare myself for this I came to believe that impaired speech is one of the most common side effects of any brain surgery.
Anyway, my point is that even people in perfect condition have very hard time speaking. Even if you are well rested, healthy and calm you and the people you know mess up a lot more words than you think.
When you rough up brain a little bit during surgery speech problems is the first thing to expect even if you never touched anything near speech centers. Even when you are just tired speech is one of the first things that get affected.
Even perfectly healthy well rested average person is awful at speaking. We are not usually aware of that because we don't pay the close attention to all little flaws.
When I observed carefully my partner after she had craniotomy to spot any signs of any possible post surgery complications I stared noticing how much other people mess up their talk.