How can Guilt overpower a man's life

i have seen alot of movie about this idea but never met anyone with such powerful guilt. I have done a lot of things in my past, and there are a few things i have done before did overpower me in specific times. This was a guilt about something that happened to a friend, or was a friend of mine. Ever since that action that i did, everytime something arose that have something to relate to it i remember my actions that day. There are guilt such as killing an innocent man that have haunted people for years. Such an event was most successfully portrayed in the movie "In Bruges" the main character was haunted by his accidental killing of a innocent kid and was never able to walk out of it. The simple mistake led to the ever lasting guilt till the of his life.