Back to the Future’s timeline shenanigans can get complicated. SometimesBack to the Future’s time travel causes paradoxes, and at other times it stops paradoxes from forming. There’s a reason why the series had so much impact on other movies about time travel, and forty years after its release, it’s still worth thinking about howBack to the Future’s time travel works.
Doc Brown warns Marty to be careful about changing the timeline, and at first, he even refuses to read Marty’s letter warning him of his death (though he does eventually read it, inspiring him towear a bulletproof vest at the end ofBack to the Future). In contrast,Marty isn’t afraid to make references to details from the futureeven while he’s in the past, from calling himself Calvin Klein to playing Johnny B. Goode before the song is released.

Marty Must Have Gained Confidence From Succeeding In His Mission As The Timeline Changed
Marty Plays Johnny B. Goode Because Of His Newfound Confidence
A fan theory on Reddit suggests thatMarty adjusts to the timeline changes the moment that they happen. While at the end ofBack to the Future, Marty is shocked by his new life, the new timeline could still have changed things for him while he was in 1955. ThroughoutBack to the Future, Marty watches the signs of his old life disappearing by watching himself and his siblings being erased from a photograph. When he fixes things and his parents' future is secured, it’s not the old timeline that has settled into existence.
Wait, What Happened To The Second Marty McFly In Back To The Future?
Back to the Future’s ending sees Marty replace another version of himself with a better life, but what happens to this version of the series hero?
This shows that something Marty brought back with him changed with the formation of the new timeline, so it’s not unreasonable to think that Marty could have changed with this as well. The theory suggests thatit’s possible that he gained memories of the new timeline at that momentand that his surprise later had to do with sorting through having two different timelines in his memory. However, it’s also possible that he became a “new Marty” without gaining memories, instead just gaining personality traits from the new timeline’s Marty.

The theory suggests thatMarty decided to play Johnny B. Goode because he has gained confidence from his new history. While succeeding in his goal might be enough to inspire him to decide that he wants to play the song, it’s also possible that his new history’s impact on his personality made him less afraid to be reckless at that moment and more willing to just have fun with it (viaSarlax on Reddit).Marty’s newly created multiversecould have created additional changes in him, on top of him having character growth throughout the movie.
Marty McFly Clearly Becomes More Confident As Back To The Future Goes On
The Changes In Marty Carry Over To Back To The Future’s Sequels
Marty begins the movie already having more confidence than his father, though that isn’t a high bar. However, there are signs when he returns to 1985 thatthis new version of Marty is more confident than he was initially in his own timeline. He didn’t send his demo tape to any record companies in the original timeline, butthe timeline has changed that in the new 1985.
This theory could also explainwhy Marty is so upset about being called “chicken” in the second and thirdBack to the Futuremovies. This isn’t something that happens in the first film, but it has a huge impact on Marty throughout both ofBack to the Future’s sequels.The reason why Marty hates being called “chicken"could carry over from Marty’s new history. In the original timeline, Marty would be used to his family being considered cowards, but in a version of history where his parents have taught him how to stand up for himself, the implication that he’s incapable of it might feel more offensive.

In the original timeline, Marty would be used to his family being considered cowards, but in a version of history where his parents have taught him how to stand up for himself, the implication that he’s incapable of it might feel more offensive.
However, it is also worth mentioning that even without the new timeline impacting his history,Marty gains confidence over the course ofBack to the Future. A large part of the plot involves him helping his father gain self-assurance, and this arc highlights both how they’re similar and how they’re different. It makes sense that it would be impossible to help someone else gain confidence without becoming a little more confident in yourself as well. Marty playing Johnny B. Goode is a highlight of this character arc.

If Marty Remembers The New Timeline, Back To The Future’s Ending Is Less Tragic
Marty Could Actually Remember This New Version Of His Family
Back to the Future’s ending can seem darkif you consider the idea that Marty is the only one who remembers his old timeline, but if he does also remember the new one, that might help soften the blow. Even if his new life seems like an improvement due to his family being happier,being the only person with memories of the family you grew up with could be very lonely. However, if Marty remembers the new timeline, the transition might be smoother.
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Marty’s memories of the original timeline are important because they highlight the importance of the changes made and how he was able to help his family during his time in 1955, which also could help Marty’s self-confidence. But the ending ofBack to the Futurefeels more like a happy ending if Marty is also familiar with the new timeline. This would mean he wouldn’t have to tiptoe around understanding his new history and could get to enjoy his new life for what it is.
