Doublethink is a term that is not often used, save when one is facing incredible hypocrisy.
For example, where one may espouse certain views with a rabidity, yet their lives and actions are contrary.
Imagine someone espousing the value of a vegetarian diet while eating a pork chop. Not just saying something like; “Vegetarianism is really healthier”, but vehemently condemning the eating of meat with a powerful voice and certainty, as they take the next bite of their pork chop.
It takes a special kind of brainwashing, a special kind of disassociation from reality to be able to perform this ‘doublethink’.
That those in the Inner Party of the government of Oceania can do this is what makes the reality of Nineteen Eighty four so terrifying.