I think the biggest problem people is that they make up ideas in an unscaleable way. People usually design a game in a very static way. They first decide on how much they want to do then make up everything they want to do. After this they start building things following an event by event timeline such as first the area near level 1 and then level 1 and so on. Essentially later on they will end up somewhere where only half their ideas are finished but they lost motivation there we got an unfinished game again. An even worse thing to do is simultaneously start on multiple areas this will just lead to confusion and hence an unfinished game. So the question is how should people work??? They should keep their game scaleable that means design it in a way that they can get a finished product fast that however is easy to extend if they have motivation left. One way to do it in my opinion for a zelda game is design the basic overworld ONLY first (that of course includes spreading items and main areas you can go to but does NOT include dugeons, cities or vast cave systems(stubs of a cave can serve a purpose here first)). After this first step you have a game that could be a bit of metroid or castlevania type of game so essentially a finished game(because all items were spread you can also easily check for warp bugs and possible sequence breakers and make sure those bugs are dealt with essentially the main overworld is done). In the next step if you did not lose motivation you can use the places you put items at as some kind of a reminder of where a dungeon or some kind of extension of the overworld might be or also where a city might be. Fill as many of those extensions in as you have motivation. Also it could be suggested to finish custom bosses before finishing the dungeon they belong in. If you have no motivation to finish the dungeon the custom boss can still enhance the experience. However if you first finished a dungeon and did not finish the boss for the level it will feel sloppy and unsatisfying.
My point is if you follow this guide if you manage to finish the overworld and bugtest it properly once finished you will have much less trouble with bugs in your game and essentially have a finished game any time of the development cycle.If you do everything by sequence bugtesting will be much harder because to check for things like sequence breaking you would have to play each dungeon in addition to the overworld before testing.
i have a hard time thinking any other way
