Final answer:
The central idea of the excerpt 'Warriors Don't Cry' is that self-preservation eliminates cruelty.
Step-by-step explanation:
The central idea of the excerpt 'Warriors Don't Cry' is that self-preservation eliminates cruelty. This is illustrated by the statement, 'Cruelty doesn't exist where self-preservation is involved.' The excerpt suggests that individuals, particularly warriors, prioritize self-preservation over cruelty, indicating that survival instincts can override any propensity for harming others.