The way I have reasoned it: The unconscious brain makes the decisions, and it does so based on very simple stuff. I felt the other day that I really didn't want to get any work done, but actually I am fairly sure I unconsciously decided that I didn't want to be in my office because the furnace is acting up and it got slightly cold/uncomfortable. Once I took care of my low level needs (layering up, putting on thicker socks, making tea) I got out of that frustrated headspace immediately.

So, create conditions for your success.