You've got a ton to accomplish today. Whether it be tasks at work or things you want to get done on your day off, you definitely don't lack in meaningful, productive content with which to fill your time.
But you find it extremely hard to get started. You stare at you tasks list. It's quite long. Maybe depressingly long. How will I ever finish all this in time? Which one do I even begin with?
These notions are often at the core of procrastination. I personally identify these notions with the feeling of being overwhelmed into paralysis. When there's too much to do, when the plate is too full, many people either delay getting started or give up completely. This is quite natural, actually, and it is not our weak character that is at fault here, but the very nature of how our brain works.
This is good news, because once we identify what causes our brain to get off track, we can develop strategies to bring it back in line and keep it happily churning the tasks we care about.