Imagine your brain is an open landscape. Its vast, open and empty. Just some green grass, flowers and bunnies etc. You can walk among this landscape and easily find anything you require. If you would like to pick a flower, it is easy to find it and see it on the ground. This is your mind as a child.
Now pretend like there are a few scattered trees here and there. They may block some vision, but they are useful. These are the things that you need to know or do, like class assignments or chores. Sometimes they are very annoying and make it difficult for you to find the right piece of information that you need, but they also produce fruit etc. Even if the trees are fairly thick, it isn't too bad because you can find everything. This is your mind when you are a tween or older child.
Now imagine that you are worrying about keeping all of your plants watered. You need some rain. When it does rain, everything continues to work as it should. You are happy, though while it is raining it is hard to find things again. Also not so pleasant. You have many more trees now because you are a teenager, though of course, when you reach college, you are aware you will have more trees, so you plant trees of worry just in case you need them ahead of time. But these worrisome trees really only block your view and soak up more water than necessary. Your landscape is not yet ready to hold so many trees.
Then, as you are fretting and worrying about more rain, you accidentally get a thick fog, instead. Everything is kept moist, we think, but there are many trees now, and this dense fog makes it nearly impossible to find anything unless it is less than three feet in front of you. The fog makes it hard for you to locate the information/trees that you need and you find yourself distracted instead with whatever thing you find in your three foot radius. You can do quite well once you push through the brain fog, or if what you need is within three feet, but it fairly difficult to locate something say, fifty feet away.
So from an outsider's point of view, if I am not thinking of the same thing they are, I will not give an accurate response because I will spout out whatever is nearest to me. If they are asking me a question and I think about something else that I know is wrong, I will stare at them blankly because I am having a hard time discovering what exactly is the correct answer. It is buried in fog. If someone tells me something important, I will gladly plant a tree for it, but I will not be able to recall it later if I wander away - which I inevitably will because I will need to search through the fog for something else in the meantime.
I also get tired much faster, pushing like that, and my eyes have trouble focusing on things because everything has to be so close.
Brains are meant to be clear of fog. Mine is not.