This is a classic, but for some reason I am completely blanking on it. Something I would have read more than 30 years ago, so late 1980s at the latest.
In the story a man wishes to buy life insurance, but he keeps getting refused. He finally gets some manager interested in why this is, since theoretically, in the worst case, they should be willing to sell insurance for the full amount plus a small markup. (That is, if someone wishes to buy $1000 in life insurance, but they might die at any time, you could still sell them that insurance if they paid $1050 for it.)
As I recall, the approval of policies is done by a computer, so they debug the program. In the end it turns out that the computer has deduced that when this man dies the world will end. Thus he is, literally, uninsurable.