Something changes in a person after midnight. Not everyone, and not every night, but often enough that it has a name in most languages - that hour when the usual defenses seem to thin out and a truth surfaces that would have stayed buried at noon. People confess things at 2 AM that they'd never bring up over coffee. Old regrets. Feelings they've been managing for months. A sentence about someone they miss that they've been rehearsing without meaning to send it anywhere.
Part of it is simple exhaustion. Holding a version of yourself together for other people takes energy, and by the time the day has drained most of it, there's less left to keep the more careful self standing guard. But exhaustion alone doesn't explain the specific shape of what comes out. It's not that tired people say random things. It's that they say the true thing they'd been quietly editing out all day.
The hour with no witnesses
Daylight comes with an audience, even when no one's watching. There are things to do, people who might call, a version of the day still ahead that has to go reasonably well. Late at night, that audience disappears. No one is expecting anything else from you until morning, which means, for a few hours, there's nothing left to perform for. The self that shows up at 2 AM isn't more honest because it's more damaged. It's more honest because it's finally alone.
This is probably why so many letters get written at that hour and never sent. Something in the quiet makes the true sentence easier to find, but the same quiet also makes it feel too large to hand to someone who'll still be there in the morning. A message sent at 2 AM carries a kind of evidence that daylight-you might not want on record. So it sits in drafts, or gets written to no one in particular, which is sometimes exactly what it needed - not an audience, just an hour honest enough to listen.