Tuning a piano is difficult due to its complexity and the precision required. A piano consists of over 230 individual strings, each tuned to a specific pitch. The strings are stretched across a large, hollow soundboard, which amplifies the sound. The task of tuning involves adjusting the tension of each string to the correct pitch, which can vary by as much as a half-step. This precision is necessary because even a small deviation from the correct pitch can significantly affect the overall sound quality and intonation of the instrument.

The difficulty arises from several factors. Firstly, the piano's strings are made of different materials and thicknesses, which means they have different tension and pitch characteristics. For example, the bass strings are thicker and have lower tension, while the treble strings are thinner and have higher tension. This variation requires a deep understanding of acoustics and the physics of stringed instruments. Secondly, the piano's action, which includes the hammers, dampers, and escapement, must be adjusted to ensure that each note is played cleanly and without unwanted resonances. This requires delicate manipulation of the action's components, which can be challenging due to their intricate design.

According to a study by the Piano Technicians Guild, the average piano has around 12,000 moving parts, making it one of the most complex mechanical devices in the home. The precision required to tune a piano is such that a single string can vary in pitch by as much as 1/100th of a semitone. This level of accuracy is difficult to achieve, especially considering the environmental factors that can affect the piano's tuning, such as temperature and humidity changes. A study published in the Journal of the Acoustical Society of America found that even small changes in humidity can cause a piano's tuning to shift by as much as 1.5 cents (a cent is 1/100th of a semitone).

In addition to the technical challenges, the psychological aspect of tuning a piano cannot be overlooked. A piano tuner must have a keen ear for pitch and be able to make subtle adjustments that can be difficult to perceive. This requires not only technical skill but also a high level of concentration and patience. The process of tuning a piano can be time-consuming, often taking several hours to complete, which adds to the difficulty of the task.

In conclusion, tuning a piano is difficult due to the instrument's complexity, the precision required to achieve accurate tuning, and the environmental factors that can affect the tuning. The combination of these factors makes piano tuning a challenging and rewarding profession that requires a deep understanding of acoustics, mechanics, and the human ear.