An unread letter can contain an apology that never gets to exist between two people.

An unread letter can hold something that never gets to happen between two people. The apology was made, the words were found, and they stayed on one side because the letter was never opened, or never sent, or arrived too late. The reconciliation existed and was never shared.

If you are holding something like that, it is worth considering whether it can still be delivered, since the window is often open longer than it feels. And if you have received something you have not been able to open, there may be more in it than you fear. Neither is easy, and both are worth a gentle attempt.