Tampering with memories is an interesting psychological trick. In ruminating, we take an already fully conceived thought and we 'infer' some new piece of information to make the thought stronger and more likely to be remembered. The trouble with thinking about things in the past with no new information is that half the shit we're thinking we just blindly made up, and yet adding new information makes it increasingly believable and therefore increasingly likely for us to remember the event this way. It really is a vicious cycle and shows us just how volatile the human mind can be.