"Thermopylae: The Battle That Changed the World"

[Jona Lendering]

why don't you believe in the Spartans having the courage to sacrifice themselves?

That's an assumptive question. The courage is not at issue. The only thing is that we don't know what happened. Perhaps Leonidas wanted to retreat, because in that way he could harm the enemy better; that cannot be ruled out, but we simply do not know. Herodotus offers a hypothesis, which must be treated as a hypothesis, and not -as is often done- as a reliable historical explanation.