The Party has an attitude of careless and contemptuous superiority towards the proles, 85% of the population of Oceania (Part II, Chapter 9) and entirely dismisses any chance that they might successfully rebel in the future. When re-educating Winston Smith after his arrest, O'Brien is bluntly dismissive of Winston's hopes in the proles:
The proletarians will never revolt, not in a thousand years or a million. They cannot. I do not have to tell you the reason: you know it already. If you have ever cherished any dreams of violent insurrection, you must abandon them. There is no way in which the Party can be overthrown (Part III, Chapter 3).
As Syme, the Newspeak expert, stated at the beginning of the book, the proles are "not human beings" (Part I, Chapter 5). Later on, Winston Smith reflects on the Party's conviction of their insignificance:
...the Party taught that the proles were natural inferiors who must be kept in subjection, like animals, by the application of a few simple rules. In reality very little was known about the proles. It was not necessary to know much. So long as they continued to work and breed, their other activities were without importance (Part I, Chapter 7).
They are by definition incapable of resistance, and thus not to be feared.
This does not, however, mean that the Party leaves the proles entirely to their own devices. As a group, they may not be dangerous, but the Thought Police still keep a few agents among them, to start useful rumors and to eliminate any natural leaders that may be born to them (Part I, Chapter 7). The proles are kept distracted by patriotic displays, manipulated news, trash literature and pornography (Part II, Chapter 3), and a state lottery (Part I, Chapter 8), so that they have less time to consider their position. They are also maintained in a state of almost complete isolation from Party members and citizens of other countries, so that they have nothing to compare their own situation with. If necessary, the Party might even raid their ranks for talent, though at the time of the novel it is simpler to just kill any proles who exhibit unusual abilities (Part II, Chapter 9).
Thus, the Party is completely sure it has the proles under permanant control, and that they pose no danger whatsoever to continued Party dominance. Since a careful reading of the Appendix on Newspeak indicates that the Party was in fact overthrown not long after the events narrated in 1984, it would seem that the casual contempt the Party entertained for the proles had the usual effect of causing the fatal underestimation of a potential rival.