As someone with ADHD, I can seriously relate to this post from Quora:

"How do we think? Profusely. I can't think of a better word to describe it.

You see, we struggle with a staggering number of thoughts and ideas. A person with a neurotypical brain has something known as “executive function,” which acts like the brain’s train conductor in that it regulates which of many thoughts and impulses get to ride on the main track. Irrelevant trains of thought are halted or rerouted so that the most important thoughts take precedence, and a main goal or key idea can sail on through to completion without interruption.

My brain has no such conductor. My thoughts are so prolific that I often interupt myself in mid-thought, with a completely different thought.

Any thought or observation can interrupt any other at any time, no matter how important or trivial either of them might be. This is because my brain doesn't weigh them at all. Instead, it treats each one as being equally important.

In a crowded room full of conversations, my brain has trouble following just one. It wants to listen to all the conversations at once and ultimately fails at being able to follow any of them.

Also, each thought resonates with associations, so, for one example, I might think “I need glass cleaner,” which leads to a memory of an old Windex TV commercial, and how its jingle, “Put On a Windex Shine,” is a rewrite of a song from Bye Bye Birdie called “Put On a Happy Face,” which leads to me playing a short clip of the song in my head several times.

When you have a lot of thoughts and each one leads to multiple associations, which may in turn lead to their own associations, it can quickly become an overwhelming cascade.

Plus, I am also compelled, with each and every interaction I have with another human being, no matter how brief or inconsequential, to dissect and examine the exchange of words and to replay all of my responses, examining each one to make sure I didn't come across as odd or strange. This can sometimes be done quickly, but if an exchange was awkward in any way I might end up mulling it over for quite a while.

We have so many thoughts to deal with, and even our thoughts have thoughts, which spawn yet other thoughts, all while our brain is constantly bombarding us with a steady stream of new (and mostly random) information, in no logical order whatsoever.

And our mental memory banks are horribly disorganized. When it comes to retrieving a memory or a stored idea (which, like our thoughts, are in no logical order whatsoever) we may locate them via a series of weird associative leaps that wouldn't make sense to anyone but us. Or, like someone with a habitually messy desk, we might just remember exactly where important stuff is at among the files, and be able to go straight to it when we need to.

The only real advantage is that we eventually learn to navigate in this torrential downpour of thoughts, ideas and memories, and to see the larger patterns in the resulting ocean of details. Eventually, we are able to see the big picture of an organization or situation, and can fully conceive and articulate its overarching functions and tendencies.

The truth is probably far more complex than what I have described here, and no two people (even ADHD people) are alike, but in a nutshell, this is a taste of how ADHD people think."

I couldn'tve said it better myself.