Normally, a callus will form on any part of the skin exposed to excess friction over a long period of time. For example, people often develop calluses on the middle finger or ring finger of their dominant hand due to writing with a pen or pencil. Another cause is from playing string instruments like the guitar or the violin; calluses will develop on the four fingers of the hand used in holding the strings down to the fingerboard, and sometimes on the fingers of the hand used for pizzicato or strumming. Weightlifters commonly experience callus on the upper-palm area due to repeated friction. Calluses are also very common on the fingers of rock climbers on almost all of their fingers. There are many activities that can result in the formation of a callus, which may even be viewed as a badge of experience and commitment to the activity.