So what, exactly, seeds low mood? Rottenberg points to three distinct but interconnected triggers: explainability, evolutionary significance, and timing. He writes:
Modern psychological theories postulate that we recover more quickly from a bad event if we can readily explain it. We would expect, then, that events that generate mixed feelings and/or confusing thoughts would be a powerful impetus toward persistent low mood.
Events that present irresolvable dilemmas on themes that have evolutionary significance — like mate choice — are fertile seeds for low mood.
When the bad things happen also matters. Extensive research demonstrates that early life traumas, such as physical or sexual abuse, lay the groundwork for a slow creep of depression and anxiety.