Why is lighting broken while using shade smooth? I have a problem with my mesh (blend file at the bottom), I want to connect these two sides of the object so the mesh creates something like a loop.
Mesh is fine and smooth if those sides are not connected, but every time I try to connect them with &quot;merge by distance&quot; the lighting on &quot;shade smooth&quot; will break and the mesh will end up looking weird. I have no idea why is that.  My mesh is not that bad (I personally think it's clean).  I was trying to make this mesh as simple and clean as I could.
Here is my blend file.
The normals of your faces are pointing in opposite directions, possibly due to a scale by -1 ?

AltN &gt; Recalculate Normals (outside) fixes that.