Throughout the events of Fallout 4, players are faced with many choices. Unlike some of Bethesda's other titles though, very few of them actually have much of an impact on the game's world and narrative. On the surface, they may seem significant, but, ultimately, much like war, the outcome doesn't really change. Sure, a companion might get mad or the reward might be different, but life goes on.
Buried amongst the myriad of possibilities, however, there are actually some important decisions to be made. They can lead to factions being wiped out in an instant or those who were once allies to the Sole Survivor turning hostile. It can be a case of life and death, although sometimes, it's simply about deciding who it is that has to die.
10 Mass Fusion
When following The Institute's questline, the Sole Survivor will learn about The Brotherhood of Steel's plans to acquire the Beryllium Agitator. The Institute also wants the device and so will ask the Sole Survivor to head over to the old Mass Fusion building to retrieve it. At this point, the player will be faced with a difficult choice.
Rather than retrieving the item, it's possible to let The Brotherhood know about The Institute's plans. Doing so will unlock the Brotherhood quest, Spoils of War. Obtaining the Beryllium Agitator for The Institute, however, will lead to The Brotherhood becoming hostile and their questline being completely locked off.
9 The Secret of Cabot House
After killing the raiders in the underrated side quest, The Secret of Cabot House, the player will be given the choice to either kill or release Lorenzo. If the player kills him, Jack will give the Sole Survivor a powerful weapon. It's also possible to release Lorenzo and then kill him immediately afterward, which will lead to the same reward.
If the player instead chooses to release Lorenzo, he will go on to kill all of the Cabot family. As a reward, he will provide the player with a lifetime supply of his Mysterious Serum. Unfortunately, these are only given out one at a time and can't be sold. Furthermore, if the player uses the Mysterious Serum to cure Andre of his radiation sickness, Lorenzo will no longer provide it to them.
8 Trouble Brewin'
Drinkin' Buddy is a modified protectron unit that is able to brew beer at an accelerated rate. If the player takes on the optional side quest, Trouble Brewin', they will be sent to the Shamrock Taphouse to track down the robot. After fighting off some radroaches and mole rats, players can find Drinkin' Buddy in the basement. Here, they're faced with a fairly significant choice.
The player can complete the quest by sending the robot to the Hotel Rexford where he will become the new bartender. Alternatively, they can choose to claim the robot for their own. If they do so, players will miss out on the caps and XP given for completing the quest, but they will be able to find Drinkin' Buddy at one of their settlements where he'll serve drinks. It's even possible to find additional beer recipes hidden throughout the game.
7 Tactical Thinking
Tactical Thinking is a Brotherhood quest that will lead to the complete destruction of The Railroad. It begins immediately after handing in the Blind Betrayal quest and will cause Railroad members to become hostile towards the Sole Survivor straight away. During the quest, the player must kill all of their key operatives, including Deacon and Desdemona.
Completing the quest will obviously make it impossible to complete any remaining Railroad quests. Depending on how far into the questline the player has progressed, this could mean missing out on the incredibly useful ballistic weave armor mod. With this in mind, for those planning to tackle this quest, it's generally better to do so later, rather than sooner.
6 End Of The Line
Tactical Thinking isn't the only quest that will lead to the destruction of the Railroad faction. If the player works their way through The Institute's questline, they will eventually trigger the End of the Line mission. Here, Father will ask the player to kill The Railroad's leader, Desdemona.
If the player fires a single shot within the Railroad HQ, the faction will turn hostile. It's possible, however, to ignore Father's request and instead warn Desdemona of The Institute's sinister plan. Doing so will lead to the player being banished from The Institute and its members becoming hostile.
5 Human Error
Covenant is an optional settlement located near the Starlight Drive-In. In order to unlock it, players will need to murder its previous occupants. This can be achieved by completing the optional side quest, Human Error, which is only accessible after hearing about Covenant from traders or settlers.
The player will first need to pass a test in order to prove that they are not a synth before being granted access. From here, speaking with Honest Dan will reveal that there's something not quite right about the settlement and players will have to choose to side with either Dan or the Covenant. There are several different possible outcomes, but it's only by killing everybody that the player will be able to take full control of the settlement.
4 A Loose End
Living within a rocky cave deep within the Glowing Sea, players will find Brian Virgil. Brian once worked for The Institute but left due to his guilt over the things he had done on their behalf. He sought refuge in the Glowing Sea and injected himself with an experimental virus that would allow him to survive the high levels of radiation. He survived but is now a super mutant.
Upon encountering the Sole Survivor, Virgil will ask them to find an experimental serum that he believes will be able to cure him. Finding the serum and giving it to Virgil will lead to him being fully cured and the player being able to loot his home. If the player does not obtain the serum or lies to Virgil, he will ask the player to kill him. It's possible to convince Virgil to take his own life instead.
3 Spoils Of War
The Spoils of War quest will only be unlocked if the player chooses to tell The Brotherhood about The Institute's plan to acquire the Beryllium Agitator. As a result, the player must effectively choose to either anger one of the two factions or to simply do nothing and instead follow a different questline.
At the very beginning of the Spoils of War quest, the player will be asked to board a Vertibird to fly over to the Mass Fusion building. This is effectively the point of no return, as doing so will lead to the Sole Survivor being banished from The Institute and hostility from its members.
2 Open Season
Although the raider gangs aren't considered one of the game's main factions, it's still possible to make them hostile. The best way to do this is by completing the Open Season quest. It's handed out by either Preston Garvey or Mackenzie Bridgeman and requires the player to execute four raider gang leaders.
As soon as the Sole Survivor kills the first of the leaders, all raiders will become hostile. There are several locations that need to be cleared out, with Nuka-Town USA being particularly difficult. It's also possible to initiate this quest without speaking with Mackenzie or Preston by simply killing any of the game's named raiders.
1 The Nuclear Option
There are several different ways of completing Fallout 4, with each resulting in at least one of the four major factions being destroyed. Following the storylines of any faction other than The Institute will lead to its destruction, while The Railroad will more than likely be destroyed at some point as well.
The most peaceful ending is reached by following The Minutemen questline to completion. If the player doesn't progress too far through the other factions' quests, it's possible to maintain a healthy relationship with both The Brotherhood and The Railroad with only The Institute being wiped out. Conversely, it's possible to wipe out three of the four factions leaving only The Minutemen behind.