Q: I was told a DM gives the illusion of free choice, but all doors eventually lead to the same room.  A: Sometimes.  But it doesn't have to be that way.  Here's what I do. I often use a flow chart approach, where loose plot points are expressed and when certain conditions are met, they move along to other branches within the story line. Otherwise writing it all out can take a considerable amount of time, and this gives them the flexibility to move about freely without restricting them to a linear approach, having to do certain things in a certain order for it to work at all. Of course, at some point the details have to be there for encounters and such, but that's what pre-made materials are for...available on a moment's notice, when needed. A real time saver, that also allows creativity and spontaneity. You're not really cheating, because the basics have been laid out, but the random element is highly interesting and everything unfolds for everyone involved...including the DM. You just have to stay a step ahead of them throughout the entire process. More importantly , this concept can also be employed for NPC dialog and development too. Other than the obvious, how much or little each NPC knows in relation to the plot, their motivations, types of things they might say, exact quotations of things they might say, how freely they engage with the players based upon how the players interact with the NPC, and, for the enlightened, how their attitude changes as certain conditions occur . This makes for very memorable adventures, when an NPC, initially viewed as a "friend" turns out to be a traitor, leading the party to their doom for payment from their arch nemesis, or other types of conditions like that. When the DM takes the time to flowchart NPC progression within the story line, it plays upon the other part of gaming that is often overlooked and under utilized..personal player emotions.  Like any good movie, make note of the emotion(s) that the players should be feeling at key points in the story line, and then determine what factors will elicit that from them. Will there be a death of a long term NPC?  A discovery that sheds unwanted light on certain aspects of the campaign?  Only you can make these determinations in order to make it happen.  Just don't force the event(s), let them occur naturally, otherwise it will appear contrived, and lose it's power at the point of impact.  A common flow for your overall campaign might begin with peace, followed by turmoil, then conflict, climax, resolution and lastly hope to continue on. This technique can even be employed early in the campaign, to motivate the players to 'get revenge', 'make things right', 'get answers', etc, and if done right, stir those personal player energies that bring out the best in every gaming session.  It is highly important that the decisions you make here are clear to the players.  What the NPC says, what they do must convey the right information.  Nothing is more annoying than seeing that the writer of the movie script is the only one crying their eyes out in the theater, because they know all the important information, but no one else feels that way, because the important information, that they needed to have, wasn't properly or fully conveyed.  When you assist your players in making that emotional   connection, between their characters and the story, the game literally comes alive, it will then become personal, they will take stake and more interest in your work, and you will have truly done your job as a great, master storyteller.