No matter how good the lost thing is, it will be a thing of the past. You can't keep it or get it back.

What you lose doesn't mean that you lose it. "It" has no value. "It" is just a new owner.

Tomorrow's yellow flowers refer to chrysanthemums after the Double Ninth Festival. It is often used as a metaphor for reports that have lost news value or things that have lost their timely role.

Let's look at it again. "No matter how good the lost things are, they will become a thing of the past." The former is relatively emotional, and the communication with the latter is not appropriate, or the latter is not enough to reflect people's own feelings, and imposing it will only play a role of restraint.

by the way, don't mind if I say something wrong. I'm just interested.