Every human being lived ...

Every human being lived behind an impenetrable wall of choking mist within which no other but he existed. Occasionally there were the dim signals from deep within the cavern in which another man was located so that each might grope toward the other. Yet because they did not know one another, and could not understand one another, and dared not trust one another, and felt from infancy the terrors and insecurity of that ultimate isolation there was the hunted fear of man for man, the savage rapacity of man toward man.
Every human being lived behind an impenetrable wall of choking mist within which no other but he existed. Occasionally there were the dim signals from deep within the cavern in which another man was located so that each might grope toward the other. Yet because they did not know one another, and could not understand one another, and dared not trust one another, and felt from infancy the terrors and insecurity of that ultimate isolation there was the hunted fear of man for man, the savage rapacity of man toward man.
 Isaac Asimov

Quotes from the same author

A subtle thought that is in error may yet give rise to fruitful inquiry that can establish truths of great value.
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 Isaac Asimov
The saddest aspect of life right now is that science gathers knowledge faster than society gathers wisdom.
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 Isaac Asimov
Why is it, I wonder, that anyone who displays superior athletic ability is an object of admiration to his classmates, while one who displays superior mental ability is an object of hatred?
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 Isaac Asimov
Intelligence is an extremely subtle concept. It's a kind of understanding that flourishes if it's combined with a good memory, but exists anyway even in the absence of good memory. It's the ability to draw consequences from causes, to make correct inferences, to foresee what might be the result, to work out logical problems, to be reasonable, rational, to have the ability to understand the solution from perhaps insufficient information. You know when a person is intelligent, but you can be easily fooled if you are not yourself intelligent.
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 Isaac Asimov
How many people is the earth able to sustain?
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 Isaac Asimov