Back to the Future question - why didn't Doc tell Marty...

…about the car crash that would ruin his life? The crash occurring in 1985; hitting a Rolls-Royce in a drag-race; causing injuries that would put paid to any hope of him pursuing a music career (in BttF Part 2 we see old Marty forlornly strumming a guitar) and causes him financial ruin as the owner presses charges.

Considering that Marty quite literally saved Doc’s life by leaving him a note about being shot by Libyans, it seems the very least Doc could do is return the favour and figuratively save Marty’s life - why didn’t he? Since he’s thoroughly investigated Marty’s future in 2015 he should be well aware of the turning point (Lorraine certainly is, as is Biff).

Doc originally ripped up Marty’s note, so he initially thought that knowing about ones own future was bad; but he gets over this and tapes the note back together - so if this is his excuse he’s a hypocrite (and also contradicts why he’d take Marty to 2015 - to save Marty Junior from a similar screw up).

You could say that since by the end of BttF Part 3 Marty has learnt not to accept the drag race and changes the future anyway - the “YOU’RE FIRED” note disappears. But Doc and Marty have ripple-effect proof memories and the timeline doesn’t seem to operate like that - for example, since they already changed the past by destroying the Almanac in 1955, 1985a shouldn’t exist for them to got back to and oh no I’ve gone cross-eyed.

It’s best if you try not to think about it too much.

Does Brown even know about the car crash? He wasn’t present when it happened (or almost happened) - from his perspective, he skipped ahead to 2015, saw that Marty’s kids were screwups, came back to 1985 to retrieve Marty and Jennifer, brought them forward again to 2015 to fix them… it doesn’t seem to have occurred to Brown that fixing the kids after the fact is far more difficult than giving Marty and Jennifer advice on avoiding major mistakes in the first place.

Doc Brown spends quite some time in 2015 - enough to get a facelift and build up detailed knowledge about Marty Junior. Being a scientist he would be naturally curious about why Marty’s music career never panned out, and the event that wrecked it is no secret. Biff taunts Marty about it when he thinks Marty is his son - given how closely Doc must have been watching Marty Jnr knowing how his old man “flushed his life down the toilet” would surely be in his remit.

Maybe Doc has an elder’s perspective that Marty probably was not going to be a rock star anyway, and an office job is what most people grow up into. To him “not being a rock star” is quite a long distance from “flushed his life down the toilet”, although young Marty probably doesn’t feel that way.

Yeah, but we see in this episode that Marty is going to be fired from that job. IIRC, it was because he was doing some sort of illegal stuff on the side. You’d think Doc would want to stop that, and you’d also think he’d investigated the very day that Marty Jr. had problems.

But Doc instead says that both he and Jennifer turn out fine. All I can think is that maybe something really good happens later because of all that.

He thought, “What the hell.”

In fairness, Marty only goes in for the potentially-lucrative-but-illegal scheme after Marty Jr would’ve been arrested; it’s possible Doc figured Marty would’ve stayed on the straight and narrow if not for suddenly and desperately needing a lot of money.

Also, Marty sans Wild West adventure is still a hotheaded idiot.

He’s the type that would screw up his life a different way even if he was warned about any particular roadbump (or Rolls Royce). There’s not much Doc can do about that.

Doc Brown as much admits it in BttF3. After Marty starts getting angry about Maddog Tannen calling him yellow, Doc mentions the Rolls Royce and that everybody has to make their own choices in life.

Also keep in mind that Doc needs to limit his observations of Marty and Jennifer to avoid universe-destroying paradoxen should he run into a version of himself from a previous observation-making visit. Although he’s probably been to other time periods enough to determine that this is the day that shit went down, the events of the movie are probably the first time he witnessed the events of that day himself.

So his observations were probably something like “One week before: Marty is successful businessman (“turned out fine” in Doc’s eyes). One week later: Marty’s kid is in the slammer and Marty is fired and implicated in some scheme. Read newspapers to get rough timeline of events”. He then figured he only gets one shot at fixing the problem, and to make that shot count, he needs backup. Marty and Jennifer are not ideal recruits for this, but they are the only others that know about the time machine so they’ll have to do.

Then perhaps he also knows that the wreck was only part of a pattern of self-destructive behavior in Marty’s life, and that a warning against that specific event won’t actually fix things for him. For example, since he knows what happens to Marty Junior the next day, he may also know about Marty getting fired that night–he’s seen that future, and Junior’s arrest might not have prevented it in the original timeline. Just keeping Marty out of the wreck will only set him up for making even more self-destructive choices.

At the beginning of the second movie, the alternative future in which Marty avoids the wreck probably doesn’t leave him a rich, popular musician in 2015. It has a Marty who achieved just enough musical success for a spectacular burnout–he started doing drugs (no doubt being taunted into it), lost Jennifer, and maybe even died of an overdose. Fixing any one event is unlikely to help; only a major change in Marty’s character will do that, and that has to come from inside–lectures and warnings won’t do it, even from a man that Marty knows has seen the future.

This is why Doc really brought Jennifer along. It was part of his plan. He knew he would trank her. He knew that the cops would find her where he left her (after all, he had already been in that alley, observing and timing Marty Junior, so he had ample opportunity to note a patrol passing through). He knew that they would take her to her future self’s home, from which he and Marty would have to retrieve her. He used their intervention in Marty Junior’s situation as an opportunity to arrange for Marty to “accidentally” see the long-term results of his behavior, triggering the introspection that would lead Marty out of his self-destructive pattern. They were supposed to arrive at future-Marty’s house while Jennifer was still groggy, so Marty would have to go inside to get her. It was supposed to be timed so that he would have to hide inside with her, and both of them would see future-Marty’s ill-advised transaction and firing. Marty would vow to Jennifer that he wouldn’t let it happen, and that promise would change his life.

Only Marty derailed the plan by stopping to buy the almanac. That delay (plus time spent arguing about it) put Doc behind schedule. Marty missed the event he was supposed to see. Instead, his actions led to the creation of the disastrous alt-1985, a desperate scramble to avert it, losing Doc in the past, and being trapped once more in 1955. It was a harsh lesson in consequences, but not the main one he needed; that eventually came in the third movie, in his talks with Seamus and his realization that both his life and Doc’s depended on him keeping his head.

I love your idea. Getting “behind schedule” when you own a freaking time machine takes work, though. But I guess Doc didn’t really have any good excuses, and it did look like it was going to work anyways. Plus, if it didn’t work, he could always try something else later, if not for the almanac problem.

But that makes you wonder why he’d pick that moment to take them from. Unless my theory about time ripples is correct, and Marty will eventually merge into the new Marty created at the end of BttF1, and thus might not remember everything.

(If he doesn’t merge memories with new Marty, then he’s got an entire life with a competent dad that he knows nothing about. Unless Doc is giving him pointers or something.)

Yes, having Marty along at that point was part of the problem. He wanted to avoid any questions about why precise timing was critical after the task he ostensibly recruited Marty for was already handled.

It’s possible that he was also legitimately concerned about paradox effects. It depends on how quickly the changewave propagates. Consider:

  1. Doc and Marty arrive at the house, and Doc realizes they’re too late to get in position for his plan.
  2. Doc comes up with some excuse and/or technobabble for Marty, and they jump back in time far enough to get back on schedule.
  3. Marty has his epiphany, he and Jennifer get clear of the house, and they all leave.
  4. The changewave from (3) catches up to the time in (1) before Doc and Marty escape into the timestream in (2). Doc and Marty arrive at the house, and Jennifer isn’t there. This is because future Doc and Marty have already retrieved her in the past, but they don’t know that–instead, Doc figures he has miscalculated, and the cops took Jennifer somewhere else.
  5. They go look for Jennifer instead of going back in time…which means they never retrieved her, so they never go looking for her, so…

If my ideas concerning temporal hysteresis in the setting are in the right ballpark, short-range time jumps would likely present greater paradox hazards than long-range ones. Even if there is no real danger from paradoxes, though, Doc probably can’t be sure of that at this point. You can’t blame him for not risking it.