This is based on Grant Abbitt's beginner tutorials. One of the things I needed to do was inset a square to make a circle. So originally it had 8 vertices, but then after extruding it inwards, I face selected only the circle, and went under Edge->Subdivide. Clearly, it looks wrong, and even after applying the subdivision modifer, it still has an uneven surface.
May I ask why? Is it because edge->subdivide is a simple subdivision(non catmull-clark)? So after I use the edge->subdivision on my original(wrong) circle, further use of the subdivision modifier wouldn't make the circle even. Because the simple edge subdivisions have already led to the wrong topology, so catmull-clark's interpolations will not help. Just want to see if my understanding is correct.