This is a great example of Confirmation Bias. Learning about confirmation bias changed my life and how I see things.

Belief in a lunar effect, therefore, feeds on itself. When we encounter human behavior that seems out of the ordinary, or we are simply noticing the right side of the Bell curve of variation of crazy events, and we believe in the lunar effect, then we are likely to notice if there is a correlation.

For example, one night when I was working in the ER, and it was a busier than average night, a nurse commented, “Wow, it’s really crazy tonight. Is there a full moon?” The answer was no, the moon was in a completely different phase that night. When I informed her of this fact she simply shrugged and promptly forgot the whole thing. One can imagine that on other busy ER nights that happen to fall on or near the full moon that would resonate with her and confirm her belief in a lunar effect.

Confirmation bias can make it seem like there is strong evidence (anecdotal) for something that does not exist outside of our belief.