I would say that Winston's fatalism helps to become self- fulfilling because Winston has taken the form of that which he detests. I think that many of his actions are driven by the fact that Winston has a disdain for Oceanic social and political orders as well as his life, in general. The detesting of such realities has impacted him so much that he ends up taking the form of that which he hates. This might help why he keeps the diary, why he engages in the sex with Julia, and even why he has such a bizarre affinity for O'Brien. In the end, Winston has become so trapped by his hatred for Oceania and its control that he can no longer be apart from it. This is why his love for Julia cannot be fully experienced as it rose out of a condition of hatred, preventing any real and authentic bonds from developing. It is also why his fear is what ends up winning out in the end and selling out Julia. Big Brother has done a good number on Winston and the other citizens who hate the institution so much that they have become ensnared and trapped by it. They wish to be free, but their hatred has become a need, something that defines their consciousness. It is in this light that I see Winston, as someone who has become so dependent on his hatred of Big Brother that fatalism has become a part of his identity, and the reason why Big Brother wins out in the end.
Other people may have other answers, but to me, there are two really clear bits of evidence that show that Winston sort of sabotages himself. I would say that we see this first when he decides to rent the apartment over the store and second when he decides to trust O'Brien. Both of these would seem to be really rash acts in this society.
In both cases, Winston is rather blatantly committing acts that can get him killed. You would think that someone in this society would suspect that everything is a trap. Why is this apartment available to rent? Why does it have no screen in it? It seems too good to be true and Winston ought to see that. The same goes for O'Brien. It seems naive in the extreme to believe that this guy is really part of this subversive group.
I think that Winston is not suspicious enough of these "opportunities." To me, that shows that his fatalism is self-fulfilling -- he's purposely doing dumb stuff that will get him caught.