I could use some suggestions on how to deal with in game events when I specifically don't want players to waste time pursuing an objective, either because it is: A) a dead end or B) they aren't supposed to go there yet.
(A) In regards to the former: I frequently make use of false clues in a game. For example, in an investigation, I will happily provide false witness testimony (either the witness is just remembering the events wrong or they are actively lying). But I follow through on this in that, if the players decide to go down that, then I will happily follow it through to the end to their detriment.
Other times, however, in the process of providing background information on the area, I will mention that there is X present. X is obviously meaningless to their adventure and I do mean obviously but, for whatever reason, they decide to follow it anyway.
My group is made up of a collection of personalities. Some people decide to follow X because they know it will derail the adventure and they enjoy that and push others to do so. Others will do so because they think that X is important and don't pick up on the increasing roadblocks that I start putting in the way that reaching X is just not happening. It is this latter group that is the issue.
Now the solution I use (just the other day) is to eventually state, after 30 minutes of putting up with this the other day, that X is a dead end for them and it was just there for world flavour. I honestly hate doing this but I feel it becomes necessary.
We can subdivide the latter group again into two groups in that there are those that once told thank me and say they failed to pick up on the cues and move back on track. And then there are those that get frustrated and annoyed that I would even mention X to begin with and spout off (what I think is nonsense) that if I go to the trouble of mentioning X that X should be something they can interact with.
I like adding flavour to the worlds I create. However this is an issue that has come up a few times. I don't want to bookend all my flavour with things like "this is relevant and this is not" as I am describing the world. But sometimes I feel like I should.
(B) Following on, sometimes I will describe something that I don't want players to get to just yet but is an obvious part of the world (the giant castle looming over the city, etc...).
Again the same groups mentioned above get into play and decide to go from the beginning of the story to the end right off the bat. Basically level 1 characters trying to take on the end bosses which usually ends up with party members being killed and making new characters.
A few campaigns back, I essentially had a stargate that lead to this cordoned off zone. And the players spent 3 hours trying to hack the gate to open up, even after I repeatedly told them from the start that it was completely impossible to hack and they would not be able to open it at this point without essentially the magic key.
UPDATE 10/15/18 So to elaborate a bit more the game currently being played is Tales from the Loop (I was trying to keep things vague in case my players were reading this and some of them are a bit on more sensitive side and I was trying to avoid the chance of hurting feelings but I realize that is not as helpful I suppose). Before we even started I got the entire group to agree to play the characters that are kids as actual kids and not as adults pretending to be kids. This in my mind is not really that difficult. I realize that perhaps for others (and those not actually good at RPing) it is hard to play characters that are not yourself all the time. The flavour detail I inserted was that as they were walking to their original planned destination that an army convoy passed through town on its way to the nuclear power plant. That is all I said. Literally that was the entire sentence that caused this derailment. The descriptions I gave for the actual mystery they were supposed to solve were far more detailed and obvious. Then basically against the wishes of the other players two of the players forced the entire group to try to break into the power plant... those two players were basically arrested by the plant security and had to face their parents eventually picking them up from jail and sitting out the rest of the mystery that the rest of the group got back to after I let them escape the security and actually do what the original mystery was. Now the plant is where the Loop actually is located. Something they as kids and new players to this world (I am not running the vanilla fantastical world in the corebook that has common knowledge of loops and robots, but instead our real 1980's) wouldn't have a clue about. Eventually they will find this out and there will be a way into the plant to get to the loop. But this was literally the second day of the campaign (first for 5 players that session) and they decided to break into the plant... After the session one of those players basically expressed why he didn't like the campaign and that I shouldn't have mentioned the plant at all if I didn't want him to try to go there. I rebutted him by reminding him that he agreed to play the game from the perspective of a kid and why his character would at all attempt this simply based on the one line I gave. He also told me that I need to insert more red herrings into the campaign cause he thought it was too linear (I always run a linear first or second day to introduce the system and world to players) whilst also complaining that I shouldn't give clues that lead nowhere. I said I would take his suggestions in mind for future sessions. So as I was telling him future sessions will have multiple things going on at once now that the introduction is over. But that I had no idea on how to give more red herrings whilst also not giving him any dead ends... Also in regards to people suggesting that if players willfully enter areas that they are not ready for that I should "kill them." I am not against doing so and have done so before. But the same player above has taken the rule in this system that the KIDS CAN'T DIE too literally and believes that they can do what they want without consequences. I immediately corrected him on this as soon as he said it in that though they can't die they might drop out of the campaign for reasons and new characters would need to be rolled. I am not sure that this correction has been taken to heart.