We are quite used to our own rituals, funerals, flowers, sympathy cards and messages. There are many other rituals, involving singing, dancing, wakes and vigils. All of these are performed in recognition of a human need - to grieve. Grief is a reaction to loss. We most commonly think of grief in relation to the death of a person who is significant in our lives but loss and grief can be experienced in other ways.
Life changes such as divorce, or accident or illness can also give rise to grief reactions.
These are experiences of change and loss. Consider Alzheimers disease where it can be said that a partner loses the one they have known and loved for years as their personality changes and their ability to communicate slips away. Here she included as well, the loss of the person we once knew, through changes like physical separation, mental illness, and criminality. Loss of part of self. This could be a structural, physical loss, of a limb for example.