The focus of my attention does indeed change at a rate which is faster than average. If something can distract me from a task, then it usually does, at least for a few moments. But why is this classified as a deficiency and a disorder? In other words, why is directed attention considered the normal human experience?
To me, it seems obvious. My attention is considered deficient because we have constructed a society in which we expect children as young as 8 (that was the age I was diagnosed) to focus in a classroom on highly abstract topics (history, language, math, etc.) for hours at a time without issue. If a child can’t meet that expectation, then they will be medicated until they do.
But if we lived in a different society, especially one set in pre-modern times, then my kind of attention might not be considered a disorder. It could even be advantageous. How many early humans suffered a premature death because their hyper-focus on gathering berries left them oblivious to the rustling of leaves?