Even though you cut materials that are softer than the blade, microstructural changes occur along the blade edge.

When not used:
1. The steel in the blade can oxidize
2. cracks that initially existed at the blade edge propagate
3. Even in hard materials like steel, surface diffusion of individual atoms can occur

When used:
1. The edge develops microscopic erosions
2. Acids in our skin can erode the surface (corrosion)
3. Small deformations can occur along the edge
4. The edge will bend through use