Writer's block. Lack of focus. Laziness. The feeling can come in many different flavors, but they're all tied to the same, underlying issue of simply being uninspired.
Think of inspiration as the emotional equivalent of incentive. As an employee or a freelancer, you have an incentive (i.e. your paycheck) to do great work. It’s a very tangible, measurable thing that can motivate you.
Inspiration, on the other hand, is considerably more abstract. It’s a feeling, or an influence, that not only motivates you, but also makes you feel good about the work that you’re doing. And that's exactly why those moments of inspiration often come from the most unlikely of places.