"I wonder if it's true that cleaning on a rainy day makes the rain stop."
Haru murmured while looking at the window. Light rain was falling outside.
"That's an illusion of causality," Ren answered immediately. "Correlation and causation are different."
"But it worked three times in a row!"
"Three times isn't statistically significant."
Noa quietly approached. "But I understand the feeling of wanting to believe."
Haru turned around. "You believe it too, Noa?"
"More than whether I believe it, why we want to believe is interesting."
Ren adjusted his glasses. "Evolutionary psychology can explain it. Pattern recognition was advantageous for survival."
"Pattern recognition?"
"When grass rustles, it might be wind or a predator. When uncertain, individuals who assumed predator survived."
Noa supplemented. "False positives are tolerable, but false negatives are fatal."
"False positive?" Haru asked.
"Thinking it's a predator when it's really wind. You just run away, so the loss is small," Ren explained.
"Conversely, if you think it's wind when it's really a predator?"
"That's a false negative. You get eaten," Noa said quietly.
Haru understood. "So overreacting helps you survive."
"Yes. The side effect is the tendency to see even non-existent patterns."
Outside the window, the rain weakened slightly.
Haru got excited. "Look! Cleaning really does stop the rain!"
Ren said calmly, "That's confirmation bias. You only remember evidence matching your prediction."
"Confirmation bias?"
"The tendency to selectively notice only information supporting your beliefs. A basic quirk of human cognition."
Noa wrote in her notebook. "Do you remember the times you cleaned but the rain continued?"
Haru pondered. "...Now that you mention it, I don't."
"Memory isn't neutral," Ren continued. "Only impressive coincidences remain."
"But," Haru countered, "are superstitions all bad?"
Noa looked up. "Good question."
"Superstition might be a way of coping with uncertainty," Ren said in an unusually gentle tone.
"Coping method?"
"In situations you can't completely control, feeling you can do something has value."
Noa continued. "Psychological comfort. Similar to placebo effect."
"By believing, does it really have an effect?"
"If psychological stress decreases, performance improves. There's an indirect effect," Ren admitted.
Haru laughed. "Ren admitting superstitions!"
"I'm not admitting them. Just explaining the mechanism."
Noa said quietly, "But you can believe while knowing."
"Huh?"
"Even knowing it's superstition, you perform it ritually. That's not self-deception, but conscious choice."
Ren pondered. "True. If 'can I gain comfort' is more important than 'does it really work,' knowledge doesn't interfere."
Haru looked at the window. The rain had completely stopped.
"So thinking I made the rain stop by cleaning is?"
"Scientifically incorrect," Ren said.
"But psychologically beneficial perhaps," Noa added.
Haru smiled. "Then if it rains tomorrow, I'll clean again."
"Why?" Ren asked.
"I don't know if it works. But I like the feeling of doing something."
Noa nodded. "That might be an honest attitude."
"Honest?"
"Neither blindly believing superstition nor completely denying it. Acknowledging uncertainty while coping in your own way."
Ren laughed unusually. "Philosophical."
"Maybe superstition is ultimately wisdom for living in an uncertain world," Haru murmured.
"Not perfect, but human wisdom," Ren acknowledged.
Outside the window, a rainbow appeared.
"Maybe the rainbow appearing is also thanks to someone's superstition," Haru said jokingly.
"That's a physical phenomenon," Ren corrected immediately.
Noa laughed quietly. "But only humans feel it's beautiful."
The three gazed at the rainbow. Between science and superstition, the world showed complex colors.