Rephrasing the original question -
I want, and expect, to able to be effective and diligent on a task (arbitrary task) because I decide to, period. To be brief - presumably, there is some value and reason to do the task in the first place.
The question asked here could be "how do I do that?" but I want to add more to it.
If the task takes any more than a short term effort, once the task has begun, how do I (or others) avoid questioning the task itself -- negotiating with one's self about whether it is interesting, important or relevant? How does one avoid procrastination when the task has gone on so long that making deliberate effort to recall the purpose and value of the task is less motivating than before? If the task is for a personal project, and there is no one to answer to, how do you keep it from going on the back burner?
For the sake of isolating the question to the core issue, imagine a very high net worth individual, or a retired person or any other scenario where the motivation is intrinsic (i.e., not tied to survival, charity, vanity or to something in between).
For those who want specifics to address, here are a few real world examples for me.
1) (re: tedious) Many years ago as an eager new graduate in engineering I was hired on to a team that was implementing a project which was already way behind schedule. As the low man on the team I was given many tedious tasks and I stayed in that mode for about 18 months. The importance of doing well on this job (and most since) was extremely clear to me.
Had the form of motivation I am asking about been possible for me I might have been able to shave a month or more off the total effort.
2) (re: back burner) I have found the following very beneficial to me a) daily meditation b) formalized time management c) big picture management including GTD. In spite of the value of these it still is not uncommon for one of these slip off my radar for a while.
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Update/Clarification: I am asking about transcending one's feeling about a task then just doing it and doing it well, quickly and effectively. Imagine a work situation in which you have been assigned a tedious task. Or, a personal project that requires an unavoidable but uninteresting step to achieve the end goal.
Maybe the question should be: Given that not all required tasks are personally interesting and valuable, how does one decouple those feelings then take on the task with some level of aggressiveness (I mean not dawdle) that may be required?