Your Piano is made up of approximately 14,000 parts that must all work together properly to produce the sound that it was designed to make. Over time and with use parts will wear, break and move out of adjustment. When you have your piano tuned the qualified technician should also perform an inspection of your piano and inform you of any repairs that it needs to keep it working  properly and to provide you with the best performance and sound that your piano was meant to give you.