Hi Ted,
That's because honestly there really isn't any sort of simple trick to keep you going. If you really wanna make a game you just have to go for it, learn what's necessary, go through all the headaches, figure out something you really want to create and like Nike says just do it and don't get lazy or sidetracked or else you'll never finish. Think of it this way.....if game development was really that easy to do then everyone would be doing it. Yes, there's thousands of people interested in game developers but only a handful follow through, fail some, and eventually succeed unless you went to school for it then that helps by major leaps and bounds too.
This is going to get a little long but, here's what I have learned over the years with my own experiences below and these are solely based on my own thoughts which might differ from one developer to another on how they think of these type of things. If other's feel indifferent well then they can add their own advice for you to compare to my opinions about this type of topic.
RULE #1 - Kiss aka Keep it Simple Stupid
To be upfront about this there really isn't a simple game but it's more the logic and idea behind it since it's too easy to overscope and try to make a gigantic project straight away. The biggest issue with this is that there's a 99% chance unless you have the actual knowledge to finish it right off the bat it will fail and never be finished. Start off with a very quick and easy idea no matter how stupid it is just finish it from A to Z.
RULE #2 - The Devil is in the Details
It's also easy to think of something fun to throw together very quickly and even finish it if you really put your mind to it. If you have no ideas just ask your friends for ideas. There's always some little stupid game that can easily become very successful if done right. However, you might for instance start that project and the next thing you know you want to add this, then this turns into that, then that turns into another that and this and that and that and this then that and that and this and next thing you know your project goes from taking a week to complete to three years and this can kill your motivation very quickly because it becomes impossible to complete because you are adding in too much. Start with whatever you think is the very core of the game to make it fun then build around that with a few things. You can always release your game and if it does good then go ahead and add more in updates but, at least you finished it and didn't get carried away. The same for this can be said with having multiple projects. Don't do that either. Start with just one and finish that one. If you have other ideas just write them down or add them to trello and such and set it aside to work on after you finish the one you are making.
RULE #3 - Not Another Solo Dungeonist Again
Surround yourself with other Game Developers and join game developer communities. There are many of them on websites and social media and even discord. I am apart of several myself. This can help you tons! It helps to keep you motivated because you are with other people in the same exact boat as you. Granted some of them have made some games already but, at least you can talk to them and take part or get feedback and help with ideas and advice and that within itself is a huge help right there to keep you going since they're talking game dev so you see that and it triggers your own thoughts to keep going on your own project.
RULE #4 - Heart Of Glass
It's easy to give and even get feedback from anyone and everyone. However, in reality even though sometimes you have no choice but to ask other game developers for advice this can actually turn very problematic very quickly because they have the same exact mentality as you and can rip you to shreds or advise you on something and you may be fixing things forever and not finishing. I mean don't get me wrong it's helpful but just remember your end goal and that ultimately the game design is yours to create. Don't let anyone else tell you what you can and cannot do with it even though feedback can assist and certainly don't let the criticizing get you down constructive or not.
RULE #5 - Gamer to Game Developer
If you're a gamer try to play games and burn yourself out on it as much as possible. If you're distracted next thing you know you are playing games and it's a few days later. There is absolutely nothing wrong with playing games. Some devs don't and claim its a bad idea but honestly I think that's a load of horse crap. I say that because I have seen some game developers who work on game dev and 3d modeling stuff claim they don't play games but then later on down the road they slip up and talk about a game they last played. The proof is in the pudding. What I do is i'll play a game every so often because I just have always been a gamer since the atari days but I will play for only a bit then get bored and go back to game development to get it out of my system so I can focus. I have gotten to the point that I can get bored of a game in about 30 minutes and then I wanna start working on game development stuff whereas I used to play for hours and days on end. This was part of the reason I never finished or got into game development even though it was a dream of mine because I was so distracted and not as serious about it. You just have to force yourself to realize it. Granted you won't really get an ideas from playing but at least you are having some fun to cool down for a bit so that you can see what someone else was able to create, think hey I wanna make something like this too even though you don't really want to copy too much especially if there's lots of clones, then get back on the horse to ride again. Plus you're supporting your fellow game developers in the process so there's absolutely nothing wrong in my opinion.
RULE #6 - Like Nike Says, Just Do It
We all have our excuses. I'm tired. I didn't sleep. I had a doctor appointment. I had to stop a burglar from breaking into my neighbors house. My kid is sick. The house caught fire. My computer sucks. I don't know how to create a 3d model of a box. Bottom Line...regardless these are all excuses, excuses, excuses even when they seem legit we as humans have a nature to try to justify anything we do but, truthfully they're still just flat out excuses no if's, and's, or but's! Stop making excuses, figure out something somewhat simple you can actually do and create it! Nobody is going to do it for you unless you're really lucky and found a good team to work with but I have tried that and never found anyone serious enough because the problem with that is that everyone has their own ideas so if you're working on something else that your heart really isn't that much into then chances are you won't be very serious or motivated to continue it therefore it will eventually fail. Regardless, ignore the riff-raff and just finish your idea. Do whatever it takes to learn how to make it. If needed you can always adjust the course of it to make it work somehow.