When to Write the Story
A strict design rule, which first appeared in Chapter 3, "Game Concepts," specifies that you must not write the story during the concept stage of design but only later during the elaboration stage. During the concept stage, your job is to define the
player's role and the kinds of gameplay that he will experience in that role. You may make a list of episodes or levels that you would like to include in the game during the concept stage, and you can think about what the player may do in each level, but you must not write the whole story yet. (To reiterate, you will need to lay out the structure of a branching story before you try to compute the budget for the entire project, but you should not actually write the story itself.)
We want you to wait to write the story because, until you know what gameplay the game will offer, you do not know what kinds of challenges the player will face and what sorts of actions she will be permitted to take. Even more important, you don't yet know what sorts of actions she won't be able to take. It's easy to write a story that includes too many different kinds of actions—actions that the programmers may not have time to implement in software. If you've written a story that includes the player's avatar riding a horse as well as traveling on foot and only later decide not to implement horseback riding for technical reasons, you've wasted a lot of time.
The task of writing the story falls into the second major stage of game design, the elaboration stage. You should begin writing after you define the game's primary gameplay mode, and preferably after you define all the major gameplay modes you will offer, because the details of those modes will tell you what sorts of actions the player can take and under what circumstances. In reality, writing the story will be an iterative process that takes place in conjunction with level design because level design creates the moment-by-moment sequence of experiences that the player can go through. If a game presents narrative only between levels, you can write a story with large granularity, in pieces after completing the design of each level, or even after all the levels are designed. But if narrative events can occur within a level, then you must write the story as you design the levels.