Today I woke up after a bad night's sleep with a nasty crick in my neck and a mountain of work. Under most circumstances it would be a "let's just skip the workout" kind of day, but this is the beauty of committing to a plan, you remove all the wasted mental cycles of "should I workout, should I skip a day and try to catch up later, should I just eat a bag of cookies and call it a day, etc..."
When you're on a plan and your fully dedicated to it, the question doesn't even arise. Should I workout today?" is about as relevant as "should I put on underwear today?" Of course, because that's just what you DO man!
This is the real beauty of choosing to live your life by a creed. When the rules of the road are laid out, you free up mental energy on making progress. Just choose a worthy creed and the rest follows!