The inverted U shaped curve of productivity

Over the years I discovered that there's a inverted U-shaped relationship between how many things I need to do and how productive I am. With almost nothing to do I also get nothing done, because I'll be procrastinating forever before I do that one thing that I need to do. The past few weeks I discovered that having too many things on my To Do List is also not beneficial for my productivity, because I just don't know where to start. When I am trying to write I am constantly obsessing about all the other things that need to happen in too little time... And running three experiments at the same time makes it hard to not get sloppy. I'm trying to go back to the optimal amount of things on my to do list to be super efficient again!