Drawing "without a net"

I'm trying to relax and just sketch without first blocking in with pencil.  Hard to explain why this is unnerving, especially as I would like to loosen up my style.

I've been keeping a sketch book with me through the day and if I have a few minutes, lay down some ink.  The other day I was early for a meeting and poked my head into the garage behind the client's offices and sketched this lonely, out of work sidewalk plow.