5 Stages of Grief – There are 5 psychological stages (normally) for someone to accept with reality. This normally happen to someone who lost someone he/she love so much. This stages was developed by Elisabeth Kübler-Ross in 1969. On her book On Death and Dying she define 5 stages for someone to finally accept situation / reality which is denial, anger, bargaining, depression and acceptance.
- Denial
First stage of grief start with denial. When we lost someone we love we usually unable to accept reality that the one we love just pass away. Some people even act as if nothing has happened. - Anger
Second stage involve uncertain feeling which cause anger. - Bargaining
Bargaining is when we start to make deals with ourselves. For some they make deals with God, accepting what just happened is beyond their control. - Depression
At this point we might feel that what was happened is just unfair. Some will think that their life has lost its meaning. - Acceptance
After some moment we finally able to accept everything that happened. Their grief, pain and scare gradually eroded.
This process could take months to years for someone to finally accept reality and relieve their pain.
Well not everyone has same step to cope with reality. Some might have a lot of time stuck in denial or anger step. Another probably will spend a lot of time in depression. So this step is a way to simplify grief process and to make it easy to understand topic.

For better understanding of this topic I include video from adult swim below. Pardon me for language.
Image source:
speakinggrief.org