For me, the most important thing about hobbies, pastimes, or what I call "play" is to have fun. When I cease to have fun, I realize I should move on, at least for some time.
But, of course, fun is subjective. I have fun playing videogames, I have fun setting up stuff on my Raspberry, I have fun configuring XFCE to behave like Win95, I have fun reading.
But sometimes, I don't feel "fun" when reading so I stop. Sometimes a videogame drags for so long I stop having fun. Sometimes I get fed up with configuring a piece of software, so I stop. Because that feels like work. Even playing Minecraft, after a while, starts feeling like work. So I stop.
Then I forget about it and some time later, I will have the urge to come back to it. Be it reading The Hobbit (yes, I'm sorry, I will finish you), playing GTA or configuring a Gemini server to my liking. And it will be fun. Until it lasts. Then rinse and repeat.
Very often I feel guilty for not finishing my hobbies. Go to the end of a long videogame, keep working on an Open Sourced project, finish a game from a Game Jam, or even keep writing a series of posts in my blog.
I got a book 📙 (I need to find the title again) talking about starting stuff without finishing it is not that bad. The pleasure is in doing, not in finishing, for some stuff, for some people.
So I try to relax with by hobbies and stuff I do in my spare time... I try, I said, he =)