What common occurrence during middle adulthood causes one to start thinking about his or her own mortality?

Our parent's death

Explanation:

According to psychology, a common occurrence that happens during middle adulthood is our own parents death, this fact usually creates a change in our thinking making us realize that we are the next in line in terms of dying and this fact usually confronts us with our own mortality and what we have done with our lives so far now that our parents are gone.

Therefore, a common occurrence during middle adulthood that causes one to start thinking about his or her own mortality is our parent's death.