Open Ended choices are a necessity to come up in RPGs at times. There is simply no avoiding situations where the PCs have a blank slate in front of them - or just a problem - and all the options in the world open to them for how to overcome this obstacle. It is a chance for the Players to show their full creativity. However, it is also prone to bringing the game to a screeching stop if not worse if you, the GM giving the choice, are not ready for what it means when you give an Open Ended Choice to your players.
How We Think It Will Work
The idea is simple. It is the core essence of how RPGs should work. You provide a situation to your PCs, and they tell you what they do and the game goes forward from there. If the obstacle is in the way, the PCs tell you how they try to overcome it. If the choice is more about where they're going, they tell you which way. Easy, right?
Well, kind of...
How It Goes Over
Frequently what happens when an open ended choice is given out - especially in what could be a tense situation - is the game freezes. The Players presented with a simple "what do you do?" either freeze and look around like they were caught not having done their homework, or they start asking all sorts of questions that have at best limited relation to the situation you have in your mind. So what is going on?
In Your Head vs. In Their Head
The first problem, and the reason for all the questions and some of the freezing, is how the picture looks. You likely have the whole scenario in mind and know what everything looks like and what the relevant information is. This is easy for you, because you built the scenario. In the players head it may look completely different. And odds are it is not a complete picture.
The second problem is option paralysis. With every option open to the players (perhaps hyperbolically but you get the idea) choosing one option can be near impossible. This is especially true when there is a feeling of a choice being potentially wrong. If your players are creeping around and come upon a strange box in the middle of the road there are potential wrong answers. Which means the obvious choices - go and check it out - could lead to potentially bad results. Very often the players are frozen because they fear a wrong choice could cost them their character - or someone else's character. Other players are afraid of being ridiculed or mocked by their fellow players for doing the "stupid thing" that triggered an obvious trap.
Players Are Not As 'In Game' As They Should Be
Sessions tend to be 4 hours long. That is a long time to be in game, and frequently players will fall in and out of game as a session goes on. If one person is talking for a long time - especially if there is no change in the tone of voice - some people will check out. Even if they're completely interested in the game, the constant stimulus in unchanging tone/pitch from one person just turns into noise and their brain goes to check other things. It is essentially the 'falling asleep in class' problem, just for fantasy pretend games.
How is this a problem? Because the player knows they're supposed to do something, but they don't know what, and they don't fully understand the situation. Only they don't want to ask questions or clarify because they're worried they'll come across as uninterested in the game or otherwise not engaged because their brain slipped out.
How To Be Ready?
So three problems, how can we be ready for this? First, be ready to answer questions, and when answering your questions keep in mind that your players don't have the benefit of picturing the scene in their head with the same clarity you do. Be kind to questions and give full answers. Point out what the important information is. And when players ask about doing potential actions, ask them what their hoped for results will be and work with them on achieving those.
Whenever possible be able and ready to summarize the situation in short, distinct points as a sort of summary. "In summary, there is a gift wrapped box in the middle of the road sitting there. You don't think this is a good place for an ambush. It is definitely strange. There is no way to continue forward without going past the box, or backtracking a third of a day to go the long way adding 2 more days to your trip." This loses a lot of the drama of the narration you did, but it sums up the situation into digestable bites your players can work with. It also helps bring anyone who may have missed something up to speed when their brain goes "shit, he asked a question. Pay attention!"
Better: Provide Options
An even better idea though is to never just drop an open ended question on your players. Instead, give them options with one of those options being room to go their own way. For example, with our gift box scenario you could present it as "Would you like to go forward as a group to investigate, have just the rogue go forward to check for traps, try to scan it from a distance, or do something else?"
This doesn't cure the above problems, but by giving options and ideas you give people something to latch onto and work with. You show routes forward that they can take and ways they can deal with the problem.
Don't Open Session With An Open Choice
Finally, as a word of advice, try not to open session with an open choice. Your players aren't fully in their characters yet. The game isn't fully in mind. The session has no momentum. An Open choice starting things off can be a painful, grating experience and in some cases can kill a session dead because everyone will want to do something else, or won't know what to do, and then that is your session.
A closed choice however works well here. A few limited options to get things moving. Build up some momentum. And once the game is going and people are fully in character, you can open up the choices more and more.