I think for me, it's an inability to think about the consequences or be affected by them at the moment I am procrastinating. What would happen if I can't finish my assignment? How much quality would I potentially have lost because I had so little time to do it? And I forget each time how much of a nuisance and anxiety it is to stay up late doing my assignment a the last minute, regretting that I didn't start it just a bit earlier. I too though, always find myself working at the last minute. It's almost like there's no other way I can work. I need the pressure to be finally right up against me for me to be 'motivated' to do it.
I think what helps if you want to actually try to work, is to find a specific environment that you can condition yourself to work in. When I'm in my bedroom I simply cannot work--it's a place of focussing on my hobbies and intersts--not school work. Might even feel like the entire house is not the right environment to work in. I have recently fell in love with the library and it's environment--it helps me work. Find that place, make yourself go to it, make sure you become accustomed to mostly working in that place, and soon enough it might just become habit to, and you can go there anytime and get work done.
And it's probably better to work in big chunks. If you're going to divide something up, divide it up into big pieces and try to do as much as you can in one sitting. Because if you give yourself many little breaks every few minutes, you're going to get distracted.