I saw something, I think it was shared by Josh, that said people procrastinate because they're scared of starting.  Once they're in the middle of doing work, it's not so painful.  At least, it's not as painful as they expect it to be when they are procrastinating.

Starting is hard.  Starting is scary.   Even starting the next phase of  work I'm already doing gives me cause to pause procrastinate.

What is it that is so scary about starting?  I think sometimes there is some fear of the unknown--I don't know how I am going to do this.

whatever.