I hope you are all doing better now that Monday is over!
Confused, I feel for you. That focus on Just. One. Thing.
It never ends! We did a "family project" with-our daughter on Thanksgiving weekend. She is getting a Master's in Art Therapy. She wanted all four of us--difficult child, husband, me, and daughter--to create a family art project. It could be based on a particular artist, or a style, or movement, or just random input. The idea was for all of us to participate. (And yes, she observed and I'm sure that she told the instructor that we are a dysfunctional family.

)
Sigh. Okay, so we did it. difficult child, who is now almost 18, slouched in his chair and refused to participate. We had agreed (well, the other 3 of us) to put our last name in the center of a piece of canvas, and we would each work on a different letter. difficult child did that part just fine. Then we divided the canvas into four sections and each did our own thing. difficult child just sat there. "I HATE art."
"It's not about art. It's about the project and about working together."
I suggested that he draw a random squiggle like his girlfriend taught him. They bought notebooks and drew shapes throughout. Great project. He is very good at it.
Of course, he had to argue. "She never taught me how to draw squiggles. I don't know what you're talking about!!"
He sat there for 5 more min. I let him pout. Then I drew a shape to give him the idea. He said, "She didn't teach me that. I knew how to do it by myself."
So the issue was about how I didn't know that she hadn't taught him; I didn't know that he already knew how to draw it; he didn't know that it was considered art; and there is a name for that type of design (but heck if I know what it is right now).
I realized that he will always, always, always get stuck on some weird item before he can move forward. And I was so proud of myself for staying calm.
Anyway, Confused, you will learn how to pace yourself, and how to detach from your g'sfg. You will forget that they even have problems sometimes, when they're older, and then their issues will jump right out and surprise you all over again.
You will get through this.