A sealed envelope offers privacy by asking others to respect a boundary they could physically cross.

Some boundaries hold only because people agree to be held. A flap of paper stops nobody physically, yet it works nearly all the time, which means the protection is social rather than material. Most of the privacy we live inside is like this, made of restraint rather than locks, and it lasts exactly as long as the shared agreement does.

Notice how much you rely on other people’s decency without ever naming it, and how much other people rely on yours. Then look for the seals you could honour better this week, the message not forwarded, the confidence not repeated, the door not opened. These are small, and they are what keeps the whole arrangement working.