Do you have ADHD/ADD or dyslexia? No, I don't. Maybe you just have bad concentration, sorry no offense.
I can actually understand you. I've always had the same problem throughout my life.
For me it's wanting to stick with it, and I can get intimidated by how thick a book is. It's funny because I've read many books in my life, so I guess I've made it through just fine with diligence.