Why is my sprite disappearing when I make a new material and add the Sprites-Default shader?

When the sprite's material is set to Sprites-Default, it works fine. However, when I apply that to a new material and add Sprites-Default as a shader, the sprite suddenly vanishes. Why is that? I tried modifying the sorting order of the sprite, thinking it has to do with the rendering order, but no change whatsoever. In addition, the sprite is partially visible when I set the shader to Sprites-Diffuse, so I don't understand why the original sprite shader is omitted when it comes to making unique materials.