Stammering can be very upsetting and knock a person's confidence. Joseph Sheehan compared stuttering to an iceberg, with the bumpy parts you can hear (overt parts) of stuttering above the waterline, and the larger block of how the person feels (covert parts) invisible below the surface. These people may feel embarrassment, shame, frustration, fear, anger, and guilt. These feelings may increase stress and effort making the person stammer more. Such negative feelings may be an important part of a treatment program.