It was a formal system and did not always help. But if you saw someone in black, you knew to treat them gently. Now, you may only get an afternoon off work for a funeral. Your loss is hidden from view. You are expected to get on with life and act as if nothing has changed, even though it has.
Any loss can cause grief.
Death is the one that usually comes to mind, but there are many others. Losses like divorce, being fired, a child moving out or losing a prized possession can all result in grief. Grief can resemble depression. Sometimes people are afraid that they should not feel the way they do when they are grieving. Seek help if you have great difficulty functioning in the weeks after the incident that caused the grief.