As the Cheshire Cat says: “Alice came to a fork in the road. 'Which road do I take?' she asked.
'Where do you want to go?' responded the Cheshire Cat.
'I don't know,' Alice answered.
'Then,' said the Cat, 'it doesn't matter.”
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Yes, I did read your OP.
I am trying to be helpful, not just a Cheshire Cat commentator ;)
I personally find it difficult to progress, even in a learning phase, without a clear achievable idea or a story to share.
I started with the 'just messing with it' stage too - and never got far...
Then I adapted some stories I had for each of the projects we are using for several game engines we picked up, because we've found that every game engine looks great when you are following the first tutorials - but real mastery only happens when you choose a goal, and work towards it.
THOSE projects are still going, and we learn more everyday. Maybe the general public won't see all of them, but its fun to think that we will be able to share some of this fun stuff one of these days. Maybe one quick game will be finished as a 'just for you' birthday/holiday gift. Maybe another will express an idea more completely than a blog could. Such notions keep us motivated to keep learning.
I honestly believe that the motivation to completing any long-term project begins with a desire to share and to communicate. I can't even finish a crocheted blanket without reminding myself repeatedly how much it will warm the recipient and of the affection the gift expresses. Otherwise, its just thousands of stitches, one right after another. Its a calming hobby, granted, but I always need a reason to keep going, and some one to share it with.
I understand you don't want to launch into your long-term project while in the early learning stages. I agree that it would be wise to wait on that, but I still recommend that you make sure that your learning projects express some notion that mean a little something to you because learning the ropes towards making a decent "learning project game' takes awhile to complete too, and can get kind of boring, when it isn't out-right frustrating. Its good to anticipate having something to show someone, getting some feed-back, and achieving small goals on the way toward a larger mastery of the process.
After the basics, its easier to find out how well you can work with any given engine when you have a scenario / idea to express and you look up lessons to specifically achieve those mini-goals. Those little successes really do help keep the process enjoyable.
How about doing a "To The Moon" style thing of re-creating some fun memories for your family on RPG-Maker? That should be simple enough, and give you something to share with your loved ones.
If you don't like that idea, maybe you could adapt a favorite fairy tale or mystery or sci-fi short story or make your own levels for your favorite old-style video game?