I'm not sure that the change was as profound as you describe but it did change me. I used to work in a wonderful little bookstore. The gal that owned it was wonderful and I worked there for 5 years and we got very close. She sold the store but I still saw her weekly at church - she had a wonderful husband and two young children. She was one of the most energetic people I have ever known.
She got sick - pancreatic cancer and I can't tell you how affected I was by her struggle with it and her death. 45 years old and so much life left to live. It left me rather cynical and with a sense of hopelessness - that no matter how we try, or who here needs us - death can occur, a death that to my human mind made no sense.