Stuttering could have a significant negative cognitive and affective impact on the person who stutters. It has been described in terms of the analogy to an iceberg, with the immediately visible and audible symptoms of stuttering above the waterline and a broader set of symptoms such as negative emotions hidden below the surface.[13] Feelings of embarrassment, shame, frustration, fear, anger, and guilt are frequent in people who stutter,[14] and may actually increase tension and effort, leading to increased stuttering.[15] With time, continued exposure to difficult speaking experiences may crystallize into a negative self-concept and self-image. Many perceive stutterers as less intelligent due to their disfluency; however, as a group, individuals who stutter tend to be of above average intelligence.[16] A person who stutters may project his or her attitudes onto others, believing that they think he or she is nervous or stupid.