The best kind of motivation is self-motivation.
To demonstrate this point, let's consider two scenarios you've likely experienced:
You have something you have to do. You're not excited or passionate about it, but you know you need to get it done. This feeling of obligation motivates you to work hard to complete the task;
You have something you get to do. You're interested in your task-you might have even assigned this task for yourself rather than receiving it from someone else-and you are happy to put in the time and effort to complete it.