What does it mean to "tune" a piano?
Will my piano need tuning? What is concert pitch? Can I tune my piano myself? Is it necessary?
Concert pitch (A440 - A above middle C vibrating at 440 times per second) has been universally accepted as the pitch to which all instruments should be tuned. It ensures that when instruments play together, they will all be in tune with one another. Pianos are designed and built to sound their best when tuned to A440. So when your piano's pitch drops due to lack of tuning, the quality of tone suffers.
Something happens when you don't tune your piano for a long time: every year that passes by, the pitch drops further and further away from where it should be, and it becomes harder for a piano tuner to pull it back up to its proper tension levels.
Technicians have to increase the tension of over 200 strings, which puts a lot of strain on the piano's structure. It is impossible to make such a big jump in pitch/tension and have the piano stabilize perfectly the first time. Thus, it can take a number of tunings before the pitch will settle and the piano will stay in tune.
Don't attempt any "home repairs" on your piano. Although it may appear easy to fix yourself, an innocent mistake can be costly. Let a technician do it - they have the right tools, replacement parts and expertise to do the job right the first time.