When someone predicts a specific date for some "end times" event (Armageddon, new system, rapture, etc.) and the prediction fails, why can't they just say, "I was wrong? I made a fool of myself," and go away?
Why do they always seem to come up with some explanation such as an invisible happening or an additional harvest or testing period, and then come out with a whole new set of calculations and announce a new date?
Why does anyone give them a moment's serious consideration?
In my case, when I first started studying with the WTS shortly before 1975, I had no idea that the organization had a long history of failed predictions and long-since discarded explanations. I had never heard of any of the Adventist date speculations of the early 1800s that led to Russell's acceptance of the idea of an "invisible presence" of Jesus. I had never heard of all his "confirming" pyramid measurements.
When the JWs who came to my door showed me the "time, times, and half a time" language from Daniel 7 and 12 and Revelation 12, I had never seen that phrase before. When they pointed it out and had an explanation that it was 3 1/2 "times" and tied it all in to 1914 and the outbreak of World War I, it all seemed to be evidence of great Bible understanding and scholarship. It was exciting to receive "hidden" prophetic "understanding" that only a relatively small number of people possessed. When friends told me it was all nonsense, I concluded that they weren't taking prophecy seriously enough.
It was difficult for me later to face how ignorant and gullible I had been.
While some of these "prophets" know they are pulling a scam, I think a lot of them really believe their own predictions. They really believe they have figured out the key to predicting the future. I think Fred Franz, for example, really believed that the expected new system would begin in 1975 or 1976 at the latest. When their predictions fail, they can't admit to themselves that they have spent years adding unrelated numbers onto irrevelant or erroneous historical dates. They conclude that that something significant must have happened on their prophesied date, just not what they expected.
Instead of saying, "I was wrong. I made a fool of myself," and going away, they redouble their efforts and start crunching another set of meaningless numbers and announce another date. They and their followers admit that they had mistaken expectations, but they continue to pride themselves in their zeal for the Lord's return.