3D modeling is hard, sometimes needlessly uncooperative. So many things can go OFF THE RAILS. Even if you feel more or less comfortable with 3D modeling in Blender, there are always more things that can spoil the fun.
Common 3D Modeling Problems in BlenderA subdivided object collapsing into a shapeless messTopology going haywireNon-manifold geometryBoolean ops ruin the topologySome models just explode (due to an error in the modifier stack)Bevels overshootingExported models are brokenToo many polygons to even move a vertex.or Blender just crashes