I never give up on projects, however I don't really have a long track record of projects to say that I won't in the future. I think that making outlines for all the stories I come up with during the development of my current project and keeping those in reserve to pick from once I want to start a new project helps immensely. If you only work on the best 1/20 projects that your imagination comes up with, it tends to yield better results. And I think everyone agrees that the idea you just get out of nowhere one day is better than an idea you get forcing yourself to come up with a premise for a new project on the spot, so stockpile those.
With teams, I can say there's one project that never got of the ground because of disagreements between me and the other person. Neither of us was incapable or lacking in skill or motivation, but the combination was just a poor one. S&Y on the other hand went well despite some potholes in the road.
When we're talking groups I can both say from last month's experience and from hearsay from pretty much everyone; It all comes down to recruiting the right people. People who can do what they promise and do so within schedule. Stalker&Yandere been blessed with the core trifecta of any VN (writing, sprites, coding) all being people who made their deadlines and did what they had to do. If any of those people is someone who doesn't reply or stalls indefinately it can ruin the entire project. The others are also important, obviously, but their work can usually be filled with placeholders so the others can continue for the time being.
If anyone doesn't do what they have to, they can be given additional... incentive.
If the project manager gets crappy placeholder images for their workload until they do their job and those placeholders make it into the project with their name in the credits, it can work as a charm to motivate them. Just kidding, that doesn't actually work (that well). Good management, clear schedules that the teammates agree to beforehand and a nice team-building enviroment (such as Discord) will help though.
If you're a solodev, then it will come down to focus and dedication. And knowing your own limitations, of course. In between someone who did a sloppy job on everything but their preferred task and someone who'll never finish a project because they keep re-doing, improving and rewriting their work indefinately, you'll need to find a middle ground. And tell yourself to stick to one style without improving until the project is done. If you don't, you can be redoing parts of the project endlessly without ever getting to a release.
If I'd have to give three simple guidelines to increase your chances of success for either solo or team (assuming you're the writer):
1. Write an outline of the story. Not lore, a list of your characters or actual chapters/excerpts of scenes you can already envision. A summary of the story in chronological order with all scenes and important events listed. If you can't make the story without having to worry about pacing, grammar, splitting routes etc., that's a good indication you'll hit the same writer's block x10 writing the actual story. P.S. No one will ever have to see it, so the outline can be in your native language or written as vaguely (to others) as you'd like.
2. Wait at least two weeks after having the idea before you start the project, preferably even longer. If it's a good story you'll still be enthusiastic about it then. If it's a spur of the moment thing, rather forgetable or way too heavily relying on a series you're enthusiastic about at the moment, you might find your interest fading while you're making the project. Not having started yet will be much less of a morale-drop when you find out your initial hype wasn't lasting.
2.2 You are allowed to make an outline right away to make sure you won't forget anything, however the two weeks won't start until you finish/stop writing that outline.
3. Assuming you made that outline, apply Chekhov's gun to everything. Every event, side-plot, character, sprite, CG, BG. Everything that isn't absolutely necessary is best scrapped. It's much more manageable to add a new character (thus a new sprite etc.) later than having a list of more sprites than you end up using. And with CG, those can pile up quickly if you're not careful when writing the story while many can be easily written out.
For S&Y, I wrote the story and then completely rewrote certain parts to scrap assets such as scrappable BGs and CGs. I'm glad I did because some parts were already a problem with the amount of assets we had now. And for second story; one third of the project, I wrote that while not allowing myself to add any more art assets than what we already needed for the first story, thus adding more content without jeopardising the project release.