In 1984, the Party maintains its rule by breaking down natural human relationships, like those between spouses or lovers and between parents and children, or friendship.
Winston and his girlfriend Julia represents the human spirit, rebelling against this repression. Winston is an intelligent, sensitive man, who understands the system which oppresses him, but does not have the power to defeat or outwit it. Julia's understanding of the system is more intuitive than intellectual, but they have enough in common on which to base a relationship.
Winston and Julia crave the one thing which the Party seeks to deny them: a private life. Unknown to Winston, the Party is aware of this and turns it to account. Winston's fatal move is to rent the upstairs room from 'Mr Charrington', the shopkeeper.
Another 'fatal flaw' in Winston's character is his belief in 'The Brotherhood' and his trust in O'Brien, which is ultimately betrayed.
In writing 1984, Orwell was making a cynical comment on the methods used by totalitarian regimes like Nazis and Communists, but he set his novel in London. The message is that given the right conditions, this kind of harsh, oppressive regime could happen anywhere.