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Comment by kibwen | Hacker News Reader

> Going around a bend, I saw a car in the ditch on the outside of the curve. I stopped the car, put on the hazards, and went to see if there was anyone in the car. As I was about to cross the highway a car come sliding around the bend more or less sideways.

The lesson here is this: lightning strikes twice (frustratingly, the usual idiom is as wrong as can be). In other words, if you observe an outcome and have no other data whatsoever about the conditions that produced that outcome, it is safe to assume that the conditions continue to exist to allow the outcome to happen again.

In this case, the existence of a car that has spun out around a curve is the clue that cars will continue to spin out along that curve.

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They teach Motorsport marshals in the UK to always keep the car that has come off-track between yourself and live traffic, and never turn your back to the track.

Whatever caused the accident is just as likely to cause another car to go in, ie oil or coolant on track, or even debris from the current incident.

Same applies on the roads I guess, especially in poor conditions.

I was military police in Germany for a few months and the one useful thing I learned there is that when you help another car to always protect yourself with their car or your own. So always park behind the stopped car and avoid being in direct line of traffic.

That's police training in the US too.

Also, in confrontations where you are outnumbered, keep one of the suspects between you and the rest. Discourages anybody taking a shot at you when their friend/accomplice is in the line of fire.

Didn't know that one.

This is fairly standard martial arts strategy when fighting multiple attackers as well. If you're fighting two people and keep one of them between you and the other, then it's just a one-on-one fight.

If you watch martial arts movies you should know that the attackers wait in line and only attack once the previous one has gotten a beating :). They never attack at the same time.

People with good tactical awareness make sure they never face more then one opponent at the same time. They survive to tell the tale. Down the line mediocre movie makers recreate the situation in a contrived way. Rinse repeat. Eventually the whole thing is a simulacrum. You're expecting a classic kung-fu movie battle, and that's what you get.

One very easy application of this axiom is whenever you're near water or rain and don't want to get wet. You're at the beach, climbing on rocks and you're not sure if a wave will hit you if you climb on the next rock. Is the rock wet? If so it will, if it's dry, you're fine. You're next to a sprinkler system and it's going around and you don't know if you'll get hit if you stand here, is the floor wet? And so on.

Until a bigger wave will hit the dry rock.

https://en.wikipedia.org/wiki/Sneaker_wave

The real axiom is, never trust moving water. Never.

Is it that lightning strikes twice, or that most events are not as rare and in need of as much setup as a lightning strike?

It's "better safe than sorry".

No, its “the occurrence of a rare event is an indication of the existence of the conditions in which that event occurs in that time and place, so if you have evidence that such an event has recently occurred, you should treat the place where it did as a place where that kind of event has an elevated likelihood of occurring”, which is far more specific and actionable than “better safe than sorry”.

This is a lovely example of HN pedanticism.

The English word is pedantry, not pedanticism.

It's not pedantimums to complain that you're swapping in a completely different moral.

I think the idea for the metaphor is that, if you see lightning hit a tree, you shouldn't think it is so rare that it wouldn't hit the tree a second time (as some people then think "lightning never strikes the same place twice")... it is, in fact, so rare to have hit anything at all, that it having hit that tree in the first place is maybe an indication that that tree is acting as some kind of preferential local lightning rod and it is actually likely to hit the same tree again.

https://www.theweathernetwork.com/ca/amp/news/article/can-li...

> Believe it or not, this long-held myth is far from the truth. While the odds of being struck by lightning are low, the chances of lightning striking the same place twice are high. Lightning can, and often will, hit the same spot multiple times.

Right, but this is different than if you see a tree that has clearly been hit by a bolt.

That is, seeing the strike shows that things are primed at the moment. Seeing a singed tree is not. (That make sense?)

That said, I can see how that still fits the idea.

I think other people have sort of answered it, but a more general version might be:

If you observe an extremely unlikely event, you should update your Bayesian prior about how likely that event is.

Makes sense. I was stuck with the idea that "seeing a car on the side of the road" is closer to seeing a tree that had been struck. Actually seeing it get struck would be like seeing the car actively crash.

Close in thought to each other, but still different things. Granted, I think your point still fully holds. There is a decay function for the likelihood of repeating events. And if you don't have evidence that what you are looking at is old, much safer to assume it is not and that the circumstances are still primed for it to happen again.

Repeating and periodic are not the same. Seeing a singed tree or a spun out car tells you nothing about how frequent these events are. They do tell you this place is likely to see those events, at any rate.

It's not the time, it's the unknown/unseen factor that's making it likely or unlikely. You think you are seeing lighting striking a tree. But maybe what you are actually seeing is lighting striking a lighting rod.

Lightning will not strike a TREE again because usually it destroys the tree in some way, changing it's height. But for many other things (buildings, mountains, etc), lightning will happily strike it over and over again.

Is the car in a ditch for a truly unlikely reason, or there a hidden lightning rod there? Perhaps you shouldn't assume a seemingly unlikely event won't happen again.

Lightning frequently hits the same places because they offer good paths to ground. Tall buildings, trees, etc. get hit all the time.

Definitely take this into account when driving too! Don’t just rubberneck at the victims. Check surroundings to see what could’ve caused it.

I was out on pescadero creek road and saw a guy had wrapped his 911 turbo around a tree. This particular bend would send you off a hillside if not for the trees. I slowed not just to gawk at the loss of a great car or to have sympathy for a man who just lost a valuable asset but cause I was wondering, “how did he manage that? Is something wrong with the road?” Didn’t notice anything wrong with the road but I took it slow anyway.

He probably just took the corner too hot. Waved a happy wave to him as I finished the turn slowly then revved back up to the usual fun speeds to enjoy the remaining 150 bends.

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