Some life-changing truths are counterintuitive. And that's certainly the case here: taking time to enjoy life makes you more motivated to work. Everyone knows the feeling – you see the pile of work in front of you, and each time you try to start, all you can think of is what you'd rather be doing.
So, be intentional about making everyday life worth living. If you can stop your work, do so when you're feeling stuck. Allow yourself a set amount of time to do an activity you enjoy: a walk in the fresh air, cooking, hanging out with friends, being creative, whatever it is. Pick something that is meaningful and life-giving to you.
It may seem backwards to experience the reward before the work is done, but when you are refreshed by doing what you love, your mind is freed up to accomplish your work better. Let's be real: will you ever conquer your to-do list completely? If the answer is no (s/o to college students), then give yourself permission to mix in some fun.
If you can't stop work, plan a reward for after you finish a particularly arduous task.
No matter how convincing I try to be, you probably won't believe this principle until you try it for yourself. But I'll give you an example. I have fours hours to do homework. If I go for a walk at hour 3, I get more work done and feel more accomplished than if I try to use all four hours. In short, I am more effective and motivated. A weary and depressed spirit sucks all the energy out of me, so I have learned that my work will suffer in turn if I am not more intentional about balance.
The balance between work and fun is necessary. I hope you know that work is important (see this article) but is not everything. What in your life is more important than work but often gets shoved aside?