First, I have noticed that sessioning these trails is key (an obvious statement for most of us). During the do-overs, I found it really necessary to be honest with myself. Sometimes I try to say to myself, "Oh, I missed it this ride, but yesterday I nailed it" and simply move on. Be honest with yourself. If you have the time, make sure to get it right. Starting down the trail might even put the trail in perspective, instead of "cheating" and starting closer to the difficult section. This is often the case for trails loaded with switchbacks.
Photo by Scott Morris
Next, it might be helpful to leave yourself a reminder on some sections that you have not cleaned. I have a trail close to my work that is loaded with technical moves, switchbacks and waterbars. So much, in fact, that I start to even question what I have/haven't cleaned. I started to leave a few reminders in the form of rocks (they even taunt me at times) near the uncleanable sections.
Finally, I have found rocking to music really helps. It's hard to get pumped while riding in granny gear sometimes at .5 mph. The added music does wonders for me, especially if I go semi-exhausted after a long day at work.
And about the shouts and screams that you impulsively do after you clean that impossible section, well, don't you love doing it?
Do you have any other suggestions, things you do to help you improve? Improving...that really is the key.