A to do list is not a today list. So what if tasks are not completed the same day as they are added? Why should they be? I’ve had things on my list that have been there for a couple of years before I have completed them. That doesn’t mean they’ve been scheduled for every day for two years.
I’ve heard the advice only to have three things on your to do list for one day many times before. As far as I can understand, when people say that, the just mean three large or high priority items planned per day. Because surely they have more things on their plate than just three? With multiple roles, multiple files or projects, parenthood, housekeeping and maintenance, we face a lot more than three demands on our time in a daily basis.
My “must do” high priority items for a day is usually 2-5 items, but the number of tasks scheduled for a day frequently runs to 40-60. I use a task list because there is no way I can stay on top of everything by keeping it in my head.