Someone (whose post has now been deleted for some reason) helpfully pointed me at: What’s Your Motivation Threshold?
and Overcoming Procrastination by Steve Pavlina
I'd forgotten about that post, and I'd forgotten about this particular bit of genius:
Originally Posted by Steve Pavlina
We often get blindsided by failure because we compare the success threshold to our level of motivation when we’re at our best.
you're going to constantly feel like you suck if you compare every aspect of your life to your highest-ever points. <slaps head>
So thank you very much for that, anonymous stranger...
P.S. Gotta love discussing motivation as a bonus to your success roll - how wonderfully geeky.