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But success SHALL crown my endeavours. Wherefore not? Thus far I have gone, tracing a secure way over the pathless seas, the very stars themselves being witnesses and testimonies of my triumph. Why not still proceed over the untamed yet obedient element? What can stop the determined heart and resolved will of man? (Letter 3.4)
What can stop them? Well, the forces of nature, for one—like an impenetrable ice sheet. Also, giant reanimated corpses. Those can stop man, too.