I used to be much more precious about notebooks myself. I may have also found tricks or games to play to on myself to force myself to use them without fear of mucking them up with bad sketches or poorly organized ideas.

Eventually I got over it now and just use them as places to scribble ideas and don't care if it's ugly. I find that over the years I just started caring more about getting the thing I wanted to accomplish done than making sure I had a pristine record of the thoughts that led up to it. Maybe it's an age thing.