Why is it advised not to hammer on a file?

Using a hammer on a file is generally discouraged because a file is typically made of hardened steel, which, while strong, also makes it brittle. When excessive force is applied, such as hammering, it can lead to the file shattering or breaking into pieces. This brittleness means that files are designed primarily for hand use, allowing for precise control and minimizing the risk of damaging the tool itself. The integrity of the file can be compromised if struck improperly, leading to potentially dangerous situations or the need for costly replacements.

Other choices may highlight other characteristics or concerns related to files, but they do not directly address the physical limitations and properties of the tool itself when subjected to impacts.