In the end it is down to mind control. Control of your own wayward brain. Easily distracted, easily blown off course. If you can keep on course while doing what you have chosen to do then you are ahead of the game. The hard part is when you are doing something that benefits from distraction. A buyer needs to be able to see the gems in the trash he is shown. He needs to have a gadfly mentality, hoppity skip and never alighting for too long on one thing and heaven forbid becoming too attached to it. Writers too need to be able to seek out interesting stuff. When you get too focused you miss the serendipitous interesting gems that are waiting for you out there.
But in the end you have to lash that brain down. Tie it down. Focus focus focus. It’s the only way. You have to be able to tell yourself “I can’t afford that thought’ or “That kind of thought will derail me”. If you are used to being led by whatever associative crap enters your head think again. You will have to cut a lot of it off at the source. As soon as you start meandering over the past, daydreaming flipping around. Kill it stone dead.