That clear expectations, clear division of labor, and fluid communication is crucial for team success.
That good GDD is the key. All the features of the game must be properly described, and all the assets required for the game must be listed out. If you don't know what to do, it's hard to do anything at all, and spending time on stuff you won't need later on is just wasteful and disheartening.
And to mind the scope and to overestimate the time it will take to make things. We had to diminish the scope, like, 20 times or so.