# Extruded edge problem

I am an absolute beginner with Blender. I have a question about extruding meshes. I have done a simple extrusion on a subdivided plane. However opposing corners of the model have different shaped corners. I want understand the logic behind this result.

I am using Blender 2.79

I created a plane mesh.

Subdivided the plane a few times.

Highlighted the faces I wanted to extrude.

Extruded to create a pyramid (or dish when inverted).

Result - two diagonally opposite corners have sharp edges. The opposing diagonal corners have chamfered edges. I don’t necessarily prefer either edge type. I just want to understand why Blender has produced two different results on what I feel is a uniform mesh.

I'm not a 3D scientist, so sorry if I'm not accurate enough, but f I try to say it with my own words:

3D softwares only deal with flat surfaces, smooth shading is only a trick to make the surface look round.

In real life if you begin to manipulate a quad or a ngon, it will bend, but in 3D, as 3D softwares only deal with flat surfaces, it's not possible.

In 3D, the only shape that can preserve a flat surface, whatever happens, is triangle, because whatever you do with its vertices, it will remain flat, while quads for example can't stay flat as soon as its 4 vertices are not aligned on the same axis.

So whatever you do with quads and ngons, a 3D software will translate them to tris.

What you have in your topology is quads. When you move their vertices, at one point you'll clearly see the 2 tris Blender uses to deal with the bending.

But if you take a quad and bend it, you can always divide it 2 ways: by one of its diagonal, or by the other.

So what you see is just Blender choosing a way or another. Why in a case does it choose this way rather than the other? I don't know.

That said, and as I guess it will cause problems, I think you should not have this kind of topology for your object, see below: