Staying motivated isn't easy, but it helps to remember your accomplishments -- especially the big ones -- long after you've completed them. Keep a list of those "big wins" in view to stay focused and help you drive to the next one you can add to your list. Image from Taz+Belly.
Rochelle Breen, writing at The Financial Diet, gives an example of how you can turn interests into specific wins you want to accomplish.
I have studied Japanese for eight years and written in my spare time for more than a decade. Those are my two activities. Two of my biggest achievements have been 1) Using my knowledge of Japan to guide the plans for an extremely important work event and thereby used less of my workplace's budget than other similar events that term, and 2) Landing a paid writing gig for a leading Japanese culture and language blog.
You don't have to combine two activities like Rochelle did. If you only have one skill or interest that you want to set a big win for, try coming up with two or three big wins or even one big win and a few smaller wins to stay motivated. You also don't have to relate your big wins to work, setting wins for your hobbies keeps you from feeling stuck there, too. The point is to create attainable, actionable goals that motivate you.
The 3-Item List That Unlocked My True Productivity [The Financial Diet]