A good king knows when to save his strength and when to destroy his enemies.

The line frames kingship as a practical craft rather than a moral ideal: effective rule requires judgment about when to conserve resources (troops, political capital, personal energy) and when to apply decisive force. “Save his strength” implies restraint, patience, and an awareness of limits; “destroy his enemies” implies that some threats cannot be managed indefinitely and must be ended to secure stability. The pairing suggests a balance between prudence and ruthlessness—an outlook consistent with Martin’s recurring theme that power is maintained through hard choices, timing, and clear-eyed appraisal of danger rather than chivalric posturing.