This question has been the most plaguing one in Dianetics and Scientology.
The ONLY way a thetan ever gets in trouble, the ONLY way he can get trapped or become part of a cluster is by mocking-up and making pictures of bad experiences.
And why record all bad experiences? This too is not good sense.
One can explain it by a yearning for events by havingness and other ways, but these do not factually lead to a total solution.
The real reason stems from a characteristic of a thetan. He never totally gives up.
There is, seemingly, a streak of resistance or resentment that makes a thetan wish to persist in the same place. If he cannot, he will do so covertly.