Sharpening a sword can be a challenging task that requires skill, knowledge, and practice. It is not as straightforward as sharpening a smaller blade, such as a knife, due to the larger size, shape, and unique geometry of a sword. Here are a few reasons why sharpening a sword can be difficult:

1. Blade Length and Size: Swords are longer and larger compared to typical blades, making it more challenging to maintain a consistent angle and apply even pressure along the entire length of the blade during sharpening.
2. Blade Geometry: Swords often have complex blade geometries with curves, bevels, and other features that require careful attention during sharpening. Achieving and maintaining the proper bevel angle and edge geometry can be demanding, especially for certain sword types like Japanese katana with their unique curvature.
3. Skill and Technique: Proper sharpening technique is crucial to achieving a sharp and functional edge. This includes maintaining a consistent angle, controlling the pressure, and using appropriate sharpening motions. It takes practice and experience to develop the necessary skills for sharpening swords effectively.
4. Tools and Equipment: Sharpening a sword requires specific tools and equipment suited for the task. These may include sharpening stones or systems designed to handle the size and shape of a sword blade. Having access to the appropriate tools and knowing how to use them correctly is essential for achieving good results.

Given the challenges involved, sharpening a sword is often best left to experienced professionals who specialize in sword sharpening. These professionals have the necessary knowledge, skills, and equipment to handle the intricacies of sword sharpening effectively and safely.

If you are interested in sharpening your sword yourself, it is advisable to invest time in learning proper sharpening techniques, seeking guidance from experts, and practicing on less valuable blades before attempting to sharpen a valuable or historical sword.