The Sight

The Sight is an Minutemen side quest in Fallout 4.

Detailed walkthrough
Mama Murphy insists that she can see the future while under the influence of chems and asks the Sole Survivor to procure some for her. She will ask for Jet, Buffout, Mentats, Med-X and Psycho, as well as asking for an extra-padded chair called Mama Murphy's chair. The chair can be built via the settlement construction menu, but can only be built once, and only in Sanctuary.

After each dose of chems, Mama Murphy will have a vision about the Sole Survivor's future. There are 12 possible visions that she can have dependent on which stage of the main story is currently active and which factions the Sole Survivor has joined. Some of these visions offer alternative solutions to various quest objectives, such as where to find a key to Kellogg's house during the quest Getting a Clue. It is also possible for her to fail to have a vision, generally if the main story line has been completed. Mama Murphy will only reveal five visions before she overdoses on Psycho and dies, after which the Sanctuary settlers will gather around her in mourning.

Alternatively, the Sole Survivor may pass one of two hard Charisma checks to convince her to give up chems entirely, at which point she will lose the Sight and no longer offer this service.

Bugs

 * It's possible that, when crafting Mama Murphy's chair, it will register as being built but never actually show itself or be placeable. This is a quest breaking bug that cannot be fixed, as the chair can only be made once. The only solution is to load from a previous save file and try to craft it again.
 * Once this quest advances beyond stage 20, it is no longer possible to assign a task to Mama Murphy via the workshop menu, even after she gets clean.
 * This can be fixed with the console.
 * It's possible after building Mama Murphy's Chair that she will continue to complain about needing to sit, ignoring the chair. Later, she will spawn standing on the chair and again ask for something to sit on. Moving the chair doesn't seem to help.