In 1984, why does Winston Smith hesitate to write in his diary?
In totalitarian states like Oceania, privacy is virtually nonexistent. The government seeks to control not just how people behave, but also their thoughts. The totalitarian state will not allow any spheres of privacy for the individual. This makes it easier for the state to subject all citizens to constant surveillance. Given the purported omniscience of the state, starting a journal is a very risky thing for Winston to do. If caught, he runs the serious risk of being vaporized. It is not in the least bit surprising that he hesitates before writing in his diary.
In Winston's world, setting down one's thoughts in written form is not a simple case of putting pen to paper; it is an act of subversion, an act of liberation, and an act of defiance against a state which will never truly be able to plumb the innermost depths of the human soul. In Oceania, harboring independent thoughts is cause for suspicion. Committing those thoughts to paper is tantamount to treason. Winston knows he is about to cross a very dangerous line. This is why he hesitates.
In the opening chapter of 1984, Winston is very hesitant to write in his diary for two reasons. Firstly, while it is not illegal to own a diary in Oceania, Winston risks a significant punishment if it is ever discovered by the Party. It is "reasonably certain" that he might be killed, for instance, or that he would spend at least 25 years in a "forced labour camp." His fear of being detected by the Party is, therefore, a strong factor in his hesitation to write.
Secondly, Winston hesitates because he does not know what to write. While he has prepared for this moment for some time, he is seized at the last minute with a kind of stage fright:
For some time he sat gazing stupidly at the paper.
In Winston's world, self-expression is discouraged and actively rooted out by the Thought Police. For Winston, then, having the opportunity to express himself on paper is so unusual that it causes him to hesitate.