For me the biggest blocker is just picking a task from my todo list when I don't have someone asking me (today) and I didn't leave a task half finished. If it's been >1d since someone asked me for something, I'm often fairly paralyzed for a while and it's a huge exertion to commit to a task. But when I get going I'm fine. TODO lists, gtd, calendars or AI don't seem to help me there.