It's 1985 in Hell Valley. How could this have happened? In 2015, Biff Tannen took the DeLorean back to 1955 to give himself the Sports Almanac. Thirty years later he practically owns Hill Valley with an endless supply of money until 2015 when the Almanac becomes useless. George McFly is dead, Lorraine is married to Biff, and Doc is in a mental institution. Here's a quick run through of the tangent and how it was rectified. The tangent started in 1955, where Marty goes back. He gets the Almanac back and burns it. The DeLorean, with Doc inside, gets struck by lightning and disappears as Marty watches from the street. Marty finds out that Doc is alive in 1885. This leads Marty to bring Doc back. Marty succeeds, the DeLorean gets destroyed by a train in 1985, and nothing about the future is certain, assuming Doc and his family don't screw anything up with the new train time machine. But could this horrific tangent have been avoided? Yes, quite easily. The Libyans chase Marty back to 1955 where Marty eventually ensures that his parents get together and comes back to 1985. It's October 26, 1985 and Marty is with Jennifer. Now this next part is very pertinent. Doc shows up out of nowhere and says that they have to go with him to 2015 to fix the future of Marty and Jennifer. They arrive on Wednesday, October 21, 2015. The next day's issue of USA Today reports the arrest of Marty McFly Jr. for theft while Griff and his gang deny complicity. Marty Sr. takes the place of his dimwitted son, tells Griff the answer is no, and gets Griff arrested for vandalism while Marty Jr. never goes through with the robbery that would've gotten him arrested. Time to go home, but leave the Almanac so the past doesn't get altered. Old Biff wants just that. While Marty and Doc go get Jennifer at their future home, Biff makes a stealth trip to the past with the Almanac and comes back without Marty or Doc noticing (until the alternate 1985). When Marty and Doc do find out, Marty interrogates Biff in the alternate 1985 and finds out when and where he got the Almanac (November 12, 1955 where he's picking up his car from the shop). Marty escapes and sets out on his mission that is later completed. A letter delivered by Western Union informs Marty that after being struck by lightning, Doc was sent back to 1885. Marty now has another mission that he succeeds at, though not in the way he originally planned. But what could've been avoided and how so? If going to 2015 never happened, no one would've needed to go back to 1955. This in turn would've then negated going back to 1885. So essentially the last five minutes of Part I, all of Part II and all of Part III all could've been avoided. How? By not going to 2015 to fix the future. It was in 2015 where everything started going wrong. The effort to go and fix the future was unnecessary. Sure, Marty Jr. was still going to go with Griff, and that needed to be stopped. But going to the future to fix said future wasn't necessary. Doc knows that by his philosophy the future hasn't been written. Your future is whatever you want it to be. Everyone should've just simply waited and stayed in 1985. Let's assume everyone stayed in 1985. Marty is with Jennifer and both are happy. Marty and Jennifer could've broken up, negating the events of 2015 altogether. Marty could possibly never marry, or marry early enough for the robbery to occur. Marty could've married Jennifer, or any woman for that matter, but not have any kids. Marty and his wife could've had kids without Marty Jr. being one of them by numerous possibilities such as abortion, miscarriage, Marty Jr. choosing a different lifestyle somewhere down the line, or dying prior to October 21, 2015. If any of these possibilities occurred, Doc and Marty Sr. wouldn't have to intervene. Or October 21, 2015 arrives, and Marty Sr. intervenes that day or in the days leading up to it. Also, when Doc and Marty Sr. travelled t0 2015 and Griff got arrested, they go home back to 1985. But Marty and Doc later go back to 1955 to prevent the alternate 1985, rewriting the future. So going back to 1985 after stopping Marty Jr. from going to jail in 2015 means that the future has been reset and anything can happen. Perhaps things could've worked out better had Doc let Marty keep the Almanac. But unless you've seen and been assured that the Almanac has been destroyed instead just putting it in a trash can, Marty could've come back later and gotten it back. Or Biff. And shouldn't you be more discreet. And always be near the DeLorean at all times given there's a chance you're the only people with a time machine?