You are also usually able to tell if something is wrong because when you go to Object Mode, there will most likely be a weird shading or pinching. Also in edit mode there are kinds of “codes” that lets you know you have something wrong with the mesh. Faces will get more transparent or opaque, they well change slightly if you have flipped normals, etc. Those are a bit hard to notice, but they are surely helpful and you do get used to noticing something might be wrong by those kind of subtle signs.
