One of the things I notice a lot of GM’s doing when they’re making a game is providing false choices. That is, they assume that they know how every character will react in a context, and they fall into the trap of intentionally leading decisions. Unfortunately, this can backfire quickly; if a player gets stuck in the middle of a situation where there is no good choice left, they make “false choices” under duress, and then the whole process is likely to continue to spiral toward an increasingly dissatisfying experience.
Let’s use an overly dramatic example: The protagonists and the main antagonists are fighting, and a major NPC ally gets incapacitated. Their antagonist continues to flee, after setting the building aflame. The GM shouts: “After him! He’s getting away!”.
See the false choice here? The GM has led the players into thinking that the best option is to follow the antagonist, when they may want to fight the flames or save their buddy. However, because the GM provided an additional set of information, a solid objective, they will not view the data in front of them correctly. If they leave the NPC, they will likely die. The NPC cannot continue the battle, and bringing them into another battle with the party is a risky proposition. The flames could likely be extinguished, or the NPC could be moved to safety.
The important thing to remember as a GM is that you are part of the narrative, not its sole creator. While rules arbitration and setting come down to you, players tend to enjoy their experience more when it allows them to be creative. This doesn’t mean that you explicitly avoid preparing anything at all; you can present them with problems, goals, and objectives, but you’ll have less preparation to do and more flexibility if you let them choose their own solutions, assuming that you’re familiar enough with the rules to handle all the directions that the game can go. It’s also a nice way to let the players choose what they want: if they want a guns-blazing action fest, they can quickly get all the violence they desire; but if they would prefer a social or stealthy approach, they can do that just the same. In addition, you likely won’t consider all the options that a player would, especially if they’re experienced in the setting and rules or if they’re playing a particularly unusual character.
The important things to consider, should you decide to force players down a set path, are their motivations, goals, and ideas about how the game will turn out. For instance, a good but anti-authoritarian character may not actually care to help the rebels if they don’t see improvement under the prospective new regime, and may take the side of one authoritarian regime over another in order to end the violence sooner. Likewise, an openly destructive and chaotic character could actually choose to do good deeds either as cover or because they don’t see any reason to hurt without cause, though they’ll gladly participate in a little disproportionate retribution. Some characters (or their players) won’t want to risk a confrontation in which they could have serious losses, either in terms of narrative or physical health. One character may want to retire from adventuring with a huge horde of gold, another may want to carve out his own kingdom, and yet another may just want to return to his home. In addition, some players picture the game going in different directions than the GM does, especially if the game’s introduced as a concept or if they expect it to take on a different focus. Sometimes it’s a matter of pacing; you can create false choices that constantly bounce the players between new, exciting, exotic environments but miss out on creating an attachment or depth to any of them, leaving players feeling like the campaign had a smattering of color but no real substance.