If you're into collectibles, you know how frustrating or exciting (depending on the situation) it is to be one item away from a complete set. Or, if you have a to do list that is one tick box away from being complete, you manage to find extra energy to just get it done. Research shows that this feeling is strong enough that we're willing to do irrational things to get rid of it.
So, the next time you're having trouble motivating yourself to do something, figure out if there's a way to turn it into a situation where you're close to completing a set. Granted this only works if the goal feels within reach, but over time you should be able to calibrate a system that helps you to get more done than you would have been able to otherwise.