In The Laziness Paradox, Scott Young writes about something that I've always had a hard time putting a finger on: why short-term estimations often fail and long-term plans often turn out to be inadequate.
I believe optimism, hope, ambition and all that general self-help pabulum work best as far beliefs. That is, being overconfident works best when it is a generalized ideal you use to think about the long future, not when you're planning your to-do list tomorrow.
The truth is, most people make two errors in their judgement. They are overly optimistic in the short-term, because inherent overconfidence and the illusion of control convince them they can achieve more than they can. But people are also too unimaginative about the future--we tend to imagine the future as mostly resembling the present.
I suggest two cures: first, acknowledge your short-term laziness more. If you know you're lazy, you can work around it. Most people don't because we like to think of ourselves as being industrious and in control, not easily manipulated automatons. Second, be more imaginative about the future, even small ripples can turn into big waves over time.
I often allow my imagination to run wild when thinking about the future. I really do think anything is possible. I believe that civilian trips to a colony on Mars will occur in my lifetime. I believe that the standard of living for all human beings can be vastly improved within my lifetime.
But while dreaming and believing in those dreams are big first steps, they're not enough. How to act in a way that works towards them is arguably the more challenging task.