I have run into this issue many times using smooth shading, but I still don’t understand what is causing it. I understand that quads are preferred by many, but this issue doesn’t just apply when I use tris. With the cube, it has similar shading problems, though it is all quads.
Though the blade of the knife has come out just swimmingly.
I wound consider myself a noob when it comes to Blender, so apologies if this is trivial.
I have included the .blend file so you can take a look yourself.
Tanto_Knife.blend (466 KB)