For me it's simply the fact that learning and mastering a certain part of the discipline raises the bar for what is considered interesting and impressive.
When I was learning programming it was exciting to see my program finally compile and run without errors. Now it's nothing special - I solved that "problem" a while ago and now having my program compile and run is just business as usual. And business as usual is usually boring.
Same with databases. At first it was interesting and exciting to poke around in SQL and get it to output the data the way I want it to be presented. Now? Just another tool where I write the same queries I've written thousands of times already. Boring.
Eventually I've lost interest in programming outside work as well. I can't remember the last time I've picked up a tutorial for something or decided to learn a new tool. If I do that I lose interest in half an hour tops. It just feels like more work on top of the 40 hours I do every week.
But sometimes there are exceptions. Sometimes I find out that I'm struggling with some weird problem and it irks me so much that I've decide to do something about it. And doing something about it usually means I write some kind of a program.
In the past few years I've done the following:
- fixed two bugs in two different Unity games using a decompiler (dnSpyEx)
- hacked several other Unity/Gamemaker games in the same way to remove intro logos or to deal with unbalanced gameplay elements (like the developers expecting me to grind for hours to buy something in-game or not putting save points after a tough boss)
- hacked together a solution to traverse my archive of various compressed files in order to re-compress them to a format that is more storage efficient (7z to zpaq)
- wrote a script to scrape a page that was shutting down
- wrote a script to upload what I've scraped to an another website
Some people do more in a week than what I did these past few years.
None of these were particularly grand projects and the code I've written is shoddy and not worth showing to other people.
And yet each one of them made my life somehow a little bit better. It all made me realize that I like to solve actual problems instead of trying to make up a problem and then pretending I need to solve it. And when I was solving these problems I could get lost in them for hours and enjoy the process of resolving them, even though in the end I wasn't doing anything special.
Perhaps something similar applies to you as well? Perhaps you feel like you're not motivated to work on a side project because deep down there's nothing in this project that is worth caring about? Maybe all you really need is to think about what do you actually want instead of what you think needs to be done and then act on it?