Well, it sounds like most of us like working on several projects at once. I've decided that there's a very smart reason for doing more than one project at a time.
I discovered very early that when I have something that is very difficult for me, it's best to take myself away and let my brain go to work. I'd study at night for a test the next day and when I'd wake up, my brain would have sorted things out and I'd do well on the test. It didn't work well if I'd try to cram all that information in right before the test. The same thing works when I'm sewing or knitting... or any of the other things I like to do. When I get to a difficult spot.... I set things down and go off to work on something else that's less challenging. When I come back to whatever I was working on, my brain would have figured out what needed to be done and I'm back on track.
I know I'm not unique. My DH works a couple of difficult crossword puzzles every day. He'll work on them at night, set them aside when he goes to bed and finish them in the morning after his brain has worked out the answers that he couldn't think of the night before. He's amazed at how easy the answers are once his brain has had the time to work on it.
Yup.... the brain is an amazing thing.... and it's good exercise to give it a good workout once in a while.