Fishbone diagram shows you the causes of the related problems graphically. Fishbone diagram consists of a rectangular box on the right hand side, where the effect which is to be examined is written. On the cause side of the diagram are the factors that influence the effect. Causes grow out of the horizontal line, which is the main body. There may be further smaller bones stressing more exact aspects of a certain cause.
Fishbone diagram is used to identify major or minor reasons for a specific problem and also to identify the root causes if any.
Although Fishbone diagram can determine the possible causes but it does not make clear the sequence or importance / magnitude or likelihood of causes.
Source of above image: http://www.spcforexcel.com/analyzing-cause-and-effect-diagrams