Why does the same situation affect me and not others?

Everyone is affected differently by the same situation. How we are affected by a situation is dependent on our genes (some people are emotionally more resilient than others genetically), our background (cultural, ethnic, etc.), our past experiences, how we were raised in childhood, our mental and physical health and our aspirations in life (for example, someone who wishes to be doctor or is doctor themselves, won't get as affected by watching surgery than someone who isn't doctor as many doctors have to see surgeries almost every day and so, they might be more resilient to seeing blood, injuries, etc (but i don't say that they won't get traumatized in long run due to watching it), which can easily traumatize an unprepared person when seeing them just once in whole life). It is also dependent on the role of a person in the situation. If your parent dies, you will react differently than if someone unknown to you dies.