Or maybe not. Remembering your resources, and setting a reasonable scale can be one of the most important things you do when creating a game. If you are working alone, I am going to go out on a limb and say it would be difficult to create a replacement for World of Warcraft in the next 4 weeks.
It is hard telling how many projects I have seen that haven’t been finished. It wasn’t for lack of effort and it wasn’t for lack of passion. It was usually for lack of planning. Most of them were hobby projects that were staffed by volunteers. Then life happened.
This is one of the main reasons that I recommend Scrum to most hobby teams that I talk to. This allows, if done properly, for the project to be broken up into bite sized pieces. This has a two fold effect. First off, it makes the project seem more manageable. You don’t have to create and entire world. You only have to take these pieces that are already completed and make a city. You don’t have to make 42 different kinds of buildings while designing an entire metropolis. You only have to create one building. Secondly, if someone has to leave mid project, you can ask them to finish that bite sized chunk that they are working on. Since it is such a small chunk, this seems like a very reasonable request. Once that chunk is done, then they can leave without having too profound an impact on the rest of the project as a whole.
Scrum, like I said, is about bite sized chunks. The idea being that at the end of each “story”, or chunk, should be a self contained chunk. In terms of Unity, this could be creating a Prefab for a building, or for completing a script. The Prefab or the script doesn’t have to be used anywhere, but it should be completed, tested, and ready to be used. If, for whatever reason, you can’t break something down to a bite sized chunk then most likely you don’t really understand what you are attempting to do. Remember, a story shouldn’t be creating a city from the ground up but rather there should be stories for the building prefabs and later another where you are simply using the prefabs that are all created and ready to go to create the city.
Long story short, look at the building blocks, not the model.