Diversify Your Personal Rewards
In doing this it is important to diversify. Have some short term and easy to accomplish tasks that provide a quick turn around on the feeling of reward you receive. For me this is often things like art, blogging, and exercise.
Also have some longer term, more difficult goals that require daily or weekly effort. The goals should be measurable and inevitable. For example writing a book should be the goal. Writing two thousand words a week will inevitable get you to the finish line. The quality of the book should not be the goal. That will be what it is, and in some sense is out of your control once you have decided on the process that will get you to the end, in this case, two thousand words per week.
Then there are the more difficult to measure and predict aspects of life. Being a spouse, a parent, the progress in your career. You want to find a set of rewards that are differentiated by time, difficulty, and measurability. Once you have diversified your personal reward system, even if you fall short in one or more of these areas on any given day or week, you can still point to some other area where you succeeded.