I don't. In the 1970s, you couldn't swing a cat without hitting some prophecy nut who knew for sure that the Rapture would be no later than 1981 and Jesus would return no later than 1988.
I don't know enough about psychology to know what's wrong with these people, but I know that whatever it is, it's very common.
Heck, my mother -- who is 90 years old -- tells me of revival meetings in the 1930s where the topic of the meetings was the Rapture coming within the decade.