A secret shared with one friend is a plan. A secret shared with five is an announcement.

Information spreads by arithmetic, not by trust. Everyone you tell has their own one person they tell everything to, so the count doubles quietly without anybody betraying you on purpose. Most leaks are not treachery, they are five links in a chain that was never going to hold. Deciding how many people know is the same as deciding whether it stays private.

Before you tell somebody, ask whether you need their help or just the relief of saying it. If it is relief, writing it down works. If you need help, pick one person and say plainly that it stops there.