Iolcus and Corinth
We don't get a lot of details about what Iolcus and Corinth were like, but we do know what both cities end up representing to Jason: awful, soul-crippling disappointment.
Iolcus is the city of Jason's birth. He's the rightful ruler of the place, but in the end he never gets to claim his throne. First it's stolen by his uncle, Pelias, and then, even after he goes on the whole quest for Golden Fleece to gain the crown, Pelias manages to keep it away from his nephew. After Medea murders Pelias for his betrayal, Jason is once again banished from his hometown. For Jason, Iolcus represents something that he's always wanted, but that he's just never destined to have.
When Jason and Medea take refuge in Corinth, it's a place of sanctuary. It's a haven where they're protected from all the angry people in Iolcus, still seething over the death of Pelias. They have kids there and probably build a house with a white picket fence. Soon, however Jason's ambition to be a king turns it all bad. When he sees an opportunity to join the royal family of Corinth by marrying the Princess Glauce, he totally kicks Medea to the curb. By the time Medea is through with violent revenge, Corinth is transformed from a city of hope to a city of horror.
The myths of Jason all take place a super long time ago. Even to the old guys who first wrote down Jason's story, he was a legendary hero from the distant past. Sometimes the era that Jason and his fellow heroes lived in is called the Heroic Age. Back in these days, the heroes were the sons of gods and the world was crammed with villains and nasty beasts that really needed slaying.
It's important to think about the fact that even to ancient Greeks, Jason was an ancient figure. It's pretty likely that the fact that heroes in the stories lived so long ago added to the highly fantastical and exaggerated nature of the tales. If a rumor gets passed around school long enough, it gets totally blown out of proportion, right? Well, it's the same way with myths. Someone tells another person about a cool thing somebody did, then after a thousand years of people retelling the story, it gets totally off the hook.