I'm one of those people who never breaks a promise to a friend and (almost always) meets deadlines at work, but I have a hard time being accountable to myself. I make tons of To-Do lists, but easily let myself off the hook when I feel like being lazy. I think it's fine, good even, to be lazy once in awhile and not be hard on yourself, but it also feels great (and is part of being a grownup) to feel like life and its many tasks are under control.
I've discovered that the secret to getting more stuff done in my life was to buddy up and start a "GSD Club." Mine has two members (myself and my sister) and one agenda: Get.Shit.Done.