A parent on a social media forum posts: "My child was diagnosed with a complex developmental disorder shortly after receiving routine childhood immunizations. It's too much of a coincidence. The doctors can't give me a clear reason why this happened, but the timing of the shots seems like the only logical explanation. I need a simple answer, not a bunch of complicated studies I can't understand." Which psychological factor best explains this parent's reasoning for connecting the immunizations to the disorder?

A parent, feeling overwhelmed after their child is diagnosed with a complex neurodevelopmental disorder, reads an online article that claims the disorder is caused by a single, specific environmental factor introduced in early childhood. The parent finds this explanation more comforting and easier to grasp than the multi-faceted, and often uncertain, explanations from scientists. Which cognitive or psychological principle best explains the parent's preference for the simpler, though scientifically unsupported, explanation?