Themes
Anger may in time change to gladness; vexation may be succeeded by content. But a kingdom that has once been destroyed can never come again into being; nor can the dead ever be brought back to life.
— Sun Tzu • The Art of War

Behind the line May contain spoilers.
Our reading
An editorial interpretation.
Feelings can recover, this says: anger fades into gladness and irritation into contentment. Destruction is different. A kingdom once destroyed doesn't return, and the dead don't come back. The contrast argues that irreversible losses deserve more caution than passing moods.
Context reviewed