All stringed instruments require tuning due the strings stretching and going lower in pitch as well as the wood expanding and contracting with temperature and humidity changes. Unlike a violin or guitar however, the average piano has about 225 strings, all of which need to be in perfect harmony for the instrument to sound its best. 

Voicing is the process of altering the density of the felt hammers that strike the strings. Hammers that are too soft can sound dull and muddy, while too hard can sound like breaking glass. Either state severely limits the pianists ability to play with expression and feeling. 

Each of the 88 notes in a piano are like their own little clockwork and the keyboard mechanism or “action” is comprised of thousands of individual parts. These parts are made of wood, metal, felt, buckskin leather, as well as composite plastics and carbon fiber in newer instruments.   Over time and playing these materials compress and wear which drastically affect how the piano feels.