This may be an odd sentiment to lead with after a welcome and restorative vacation, but:
The greater power of bad events over good ones is found in everyday events, major life events (e.g., trauma), close relationship outcomes, social network patterns, interpersonal interactions, and learning processes. Bad emotions, bad parents, and bad feedback have more impact than good ones, and bad information is processed more thoroughly than good. The self is more motivated to avoid bad self-definitions than to pursue good ones. Bad impressions and bad stereotypes are quicker to form and more resistant to disconfirmation than good ones... Hardly any exceptions (indicating greater power of good) can be found.
That's from Baumeister et al, in an analysis appropriately titled "Bad is Stronger Than Good." [here's the complete PDF].
It makes intuitive sense that the mind is wired to prioritize negative experiences (threats) over positive ones. It accounts for effects across a broad range of your subjective existence, from the memories you retain to your political affiliation. Prioritizing threats may be necessary for survival, but can make life miserable, particularly in an environment that is perceptually threat-rich, as media culture has become.
Why are so many of our stories structured around a hero who faces down evil, resists what seems inevitable, and emerges victorious, if changed? We don't tell those tales because we see them reflected in the natural arc of the world around us. We tell them as a bulwark against a more grim reality - that fear, sorrow, and surrender to weakness are the more common outcomes in the face of adversity.
But we keep telling the stories, and when we believe them, we sometimes follow an anomalous trajectory, a deviation from the physics in which all objects fall unperturbed into a great black hole. We resist the terrible gravity of our birthright, break the world's laws and force it to rewrite them.