The Terminator series has been a pillar of the Post Apocalyptic genre since the 80's; it's the story of Judgment Day, an apocalyptic event that can be temporarily pushed back, but never outright averted. This idea of fate, of a man-made pre-destination, is a key component of the series and it meshes well with all the time travelling that pretty much anyone can do in this universe for some reason. There is a serious flaw with Skynet, the series antagonist, though, and it's one that has its roots in the structure of good storytelling.
TL:DR, Skynet is an artificial intelligence that grew too powerful, too fast, and scared its creators. Skynet perceived its creators attempts to shut it down as a threat and calculated that all other humans would see it as a threat as well, so it fired off a bunch of nukes like Trump in the middle of a temper tantrum.
Voilà, one Judgement Day.
It fails to kill all the humans though, so there is a lengthy war fought between the human resistance fighters and Skynet's robotic forces. The war is long and bloody because Skynet doesn't just use all the biological and chemical weapons at its disposal for some reason. It starts out with the humans having to contend with primarily the bare skeleton T-800 Terminators that we're all familiar with, but pretty soon they're also dealing with the Infiltrator T-800's that look exactly like humans... as long as those humans are all competing in a Mr. Olympia contest.
Despite having a near endless army of obedient death robots and fighting in an environment that is now deadly to humans, Skynet doesn't do too well. As the war enters its fourth decade Skynet finds itself backed into a corner by the rag tag bunch of plucky human survivors.
Blame it on budget constraints or the limitations of CGI technologies, I'm still shocked that it took us 25 years to get a story set in that part of the timeline. The part of the timeline where the humans are fighting a full on war against murderous robots in a radioactive wasteland.
How? How did it take us that long to get there?
But I digress. The point in the story in which Skynet sends a Terminator back to kill the resistance leader before he was even born, while great in terms of storytelling, is really dumb in terms of actual strategy. Of all the things it could have done, of all the infinite options available to it, that seems to be the most randomly haphazard.
And now I need to take you on a slightly tangential route. There is a point to it though, so bare with me. In Dungeons and Dragons there are these little lizard things called Kobolds, and while they're a possible threat to low level characters they quickly become little more than a pesky annoyance. As more and more supplement rule books were released for D&D 3.5 though, something terrible started to happen. Through an amalgamation of disparate skills, feats, spells and reptilian companions - a single Kobold managed to turn itself into a god in an instant and break the entire game. The worst part of all this was that it was all allowed within the rules of the game, it just took some insane rule junkie Munchkin to put it all together.
(For those interested; Pun-Pun, the Kobold in question, could temporarily enhance the abilities of its reptile companion, then steal them to enhance its own permanently. Rinse and repeat ad nauseam. There's a bit more involved than that, but basically at a certain point Pun-Pun would hit critical mass and become so conceptually powerful that it would physically manifest itself in the real world... and then proceed to kill everyone around the gaming table. Totally true story.)
Anyway, I took that little tangent to show you what Skynet has access to.
The problem with time travel in the Terminator universe, for humans, is that you can only go back with your bare naked self. This means you've got however many years of experience and know-how and your swinging copulating tool with which to save the day. It's why the Terminator movies all start with a confused, naked dude running around trying to find some clothes. Sure, Jai Courtney's Kyle Reese could have jumped back to 1984 and told humanity about the glories of the iPhone, but he couldn't bring one back with him and he sure as hell couldn't tell them how to make one.
A Terminator, however, is basically just a computer on legs that's wrapped in a skin suit. You could load any and all the data you'd ever need into a Terminator and send it back to any point in time. In one of the comics, a Terminator accidentally goes back to the Cretaceous Period and gets stomped on by a T-Rex, because why not?. My only question is, why would Skynet bother sending a Terminator back to a point in time when it's not in control of the entire damn planet? In the first Terminator movie, the Terminator and Kyle Reese jump back from 2029, and considering Judgment Day was first meant to occur in 1997 - that's roughly 32 years of playtime for Skynet to mess around in.
Why would Skynet not send a Terminator, fully loaded with all the latest schematics and technologies, back to a point when it's already in control? It could be back to 2028, or even all the way back to 1998, it doesn't really matter. The point is that the technology and blueprints that the Terminator has stored in its metal head will be more advanced than what's available to Skynet at that point in time. All Skynet would have to do is hold off the resistance fighters while it upgraded itself, then just not die until 2029, and then repeat the process.
Go back, become more advanced, go back again, become more advanced again. If it did this a ten times, that's roughly 320 years of advancement in the blink of an eye. Each time Skynet would become more powerful and holding off the resistance fighters would become easier and easier. We already know it can make it to 2029 with just the basic T-800's (as well as a few other non-humanoid machines), how hard would it be to get back there with the T-1000's or the T-X's? It wouldn't only get easier because it's becoming more powerful with each iteration, but because it's also learning through the repetition of history. Ambushes could be laid, decisive losses could be avoided and pivotal battles could be won. It would never need to risk its own creation by sending a Terminator back to a time prior to Judgment Day, which in itself is an act that could potentially disrupt the chain of events that led to it being created.
The problem with this method is that it's an instant win for Skynet. Each time it upgraded, the resistance fighters of that timeline wouldn't even know that they were fighting upgraded Terminator models, they'd be too busy getting their arses handed to them. After enough of these loops, it wouldn't be unrealistic for Skynet to learn how to kill off humanity in a matter of hours after Judgement Day. At that point, it'd just be looping back again and again to save literal time.
This is where the structure of storytelling jumps in an neuters things in favour of the humans. This sort of truly apocalyptic scenario is one that you couldn't fight against, and would therefore make for a pretty terrible story. Judgment Day would come and humanity would be wiped out entirely - that's not a post apocalyptic story, it's just a straight up apocalyptic one. Skynet needs to make nonsensical decisions that a genocidal AI would never make, because humanity needs to have a slim chance of actually defeating it. The humans can get pushed back into a corner and beaten down, it can look like they'll be exterminated at any second, but at the end of the day the good guys have to win.
The upside to this castration of Skynet is that we get the great thematic notion of Judgment Day being something that is perpetually pushed back, but never truly averted. In each instance, the world ends in a different time because it got pushed back after the last time. Judgment Day has arrived, and been subsequently averted, in '95, '97, '03, '04, '05, '11 & '17 - that's not bad for humanity, it may get knocked down but it always gets back up and fixes things. In terms of storytelling, it's like an in-built retcon switch for the series, we'll always be able to have Terminator movies because Judgement Day will keep happening with each new era of technology. It's why we started with Terminators basically running on MS-Dos and ended up with Terminators that are comprised of nanobots. As technology changes, the Terminators change too, and we get another movie about another Judgement Day - because that's our fate.
Sending a lone agent back in time to try to fuck with causality is dumb, but it's interesting. Playing it safe and upgrading to the point of godhood is the smart thing to do, but it's pretty boring and near impossible to beat. As cool as that post-Judgment Day battle could potentially be, it's only cool if the humans actually win it. And I just don't think that humanity could realistically win against an genocidal AI with time travel capabilities.
Besides, does Skynet even have a plan for after it wipes out humanity? Does it even want anything? What's the end goal here?