In Terminator 1 Skynet looses because John Conner taught people how to fight the machines, but John Conner only knows this because Kyle Reese taught Sarah Conner how to fight the machines and she taught John Conner. But Kyle Reese only knows this because he was taught by John Conner- so there's no actual source of the information on how to fight the machines, it's a loop with no beginning or end.

I had a philosophy teacher who said this is evidence of divine intervention to destroy Skynet, essentially God told people through John Conner how to win, but a cut scene in Terminator 1 implies Skynet was also created by reverse engineering the chip in the destroyed Terminator- implying there's also no origin of the information on how to create Skynet and it's also an infinite loop.