It's become something of dogma that grief will follow a standard trajectory: denial, anger, bargaining, depression, and acceptance. But it's entirely possible for people to feel these in random order, or several of them at once.
Psychologist George Bonanno took up the subject in his book The Other Side of Sadness: What the New Science of Bereavement Tells Us About Life After Loss.
It received an update after ten years, but still holds to the idea that our emotions help us deal with loss--all of our emotions. George Bonanno visits the JX.