Grief is a lot like being punched in the stomach. Your initial response is to close up, hold you injury, and move away. Slowly the pain starts to lessen, but unbeknownst to you their is an underlying injury, a cracked rib. An hour, a day, maybe weeks later you will be doing a activity you have done a hundred times. But this time that injured rib moves. Perhaps it just causes some slight discomfort, or perhaps it punctures a vital organ. Thus sending you to the ground in agony and left just hoping someone will come along and help.
Grief, when ignored, will lie within you, unseen and unnoticed. Then you go about your life, doing something you may have done a hundred times before. But this time it triggers a memory. Perhaps you will tear up a bit, then sit for a moment to compose yourself. Or, perhaps, it will throw you into a rage. You might then lash out at whomever is near you, whether they are friends, family, or complete strangers.
Grief, in it's essence, is unpredictacle and involuntary. That is until you learn to address it, express it, admit to it. Realizing grief is not weakness was my first step. After that, allowing my daughter to witness my grief seemed to give her permission to greive as well. From then on it has been easier for both of us to be honest about our feelings to each other.