One of the many challenges that has resurfaced in my life over and over again is a lack of motivation. Not just how to be passionate about work (which has never been a problem), but how to be consistently motivated. And possibly more importantly, how to finish things.
I've done a lot of thinking (and some reading) about this. And one concept keeps resurfacing. From what I can understand motivation is how we perceive the outcome of something. meaning if I think it will be painful to put my hand on a hot stove I won't be very motivated to put my hand on the stove.
While that's such an elementary concept it may put you to sleep. It has profound implications when you look at the subtly of it. For example: if you perceive a difficult task will involve painful challenges, or worse troublesome pressure from your boss/spouse/mother/god(s) you will be less motivated to spend time on it (and more likely to procrastinate).
For now, the only practical application I can think of is to consciously shape the way I think about tasks that I am taking on. Thinking about the small tasks that can happen without much trouble makes it easier to be excited about doing them.
This also has the effect of distributing the reward of accomplishment. Which ties into another possible reason for lack of motivation: short attention span.