Do you keep a training journal? Paper? Online? Software program?
If so, what do you record in it? Do you stick to mileage and time, reps and weight? Or do you include your perceived effort, your mood, what you ate or how you slept?
Lastly, do you ever look back at what you wrote?
I keep both a paper and an online training journal. One is merely a reflection of the other (although I record a few humorous thoughts in my notebook while I'm at the gym - ie, smelly man, water fountain parade, dude who won't stop singing, etc). I look at previous workouts in order to figure out the weights to use or the rep scheme, but that's about it.
Today I completely failed that very simple exercise in due dilligence. Off the bat, I was doing my full body workout with too high a reps scheme (3 sets of 15 rather than the 10 I was supposed to be doing), and then I flubbed on the amount of assistance to set for the Gravitron.
Moral of the story is - use what you've got. Namely - if you record your workouts in a journal, READ them.