Usually when I get that, it's because I'm trying to make something perfect. To handle all the edge cases, to make something bulletproof. And then I take a deep breath and remember that the sooner I make a shitty version, the sooner I can actually figure out what I need to optimize for.<p>So take a big breath and build the shitty version. You will save so much time in the long run.
Don't over think it... Most times people get writers block when they think of style and syntax over substance. I mean programming isn't like writing a story... you don't have to make up the fact that your function has to return a string with a username... you just want to do it bad ass... just write it... I call it Jalopy Code... its the junk that gets it done and then I go back and clean it up after...