According to Theravadin Buddhism it is not all or nothing, people can be partly enlightened. And there are clearly defined levels of enlightenment, just like there are clearly defined levels for things in our regular society. If you go to a college for two years for a four year course, you don't get a degree just because you went to college for two years. Partly enlightenment has a definition.
I mentioned them the other morning so I'll just talk a bit more about the first level, "Stream-enterer". The first level is that one has complete faith, complete confidence in the Triple Gem, and that this is the path leading to the ending of all suffering. A person who has reached the first level of enlightenment is not attached to rights and rituals and has had a deep insight into the non-personal nature of self, that is, the third characteristic "Anatta". So if one thinks one is partly enlightened just because one has a little bit of an insight, that is not the case.