We started developing software with grandiose up front plans with durations of several months. We defined sprints, each with several goals and each going on for several weeks.
Does this surprise anyone?
I consider myself to have a good attention span. I can concentrate on a single problem for hours (if I’m not interrupted externally, anyway) and not only forget the time but also make good advances in a project.
However, I cannot focus on a single task for weeks and weeks. Days are maybe possible. Building a product requires much more time than that. This means that the development should be divided up onto a multitude of mini-sprints, each having an easily understandable motto which focusses and thereby motivates everyone involved.
Keep the implemenation time of the minimum lovable product below two months, or else you’ll most probably set yourself up for failure.