"Just like a red, blue, or white lotus — born in the water, grown in the water, rising up above the water — stands unsmeared by the water, in the same way I — born in the world, grown in the world, having overcome the world — live unsmeared by the world. Remember me, brahman, as 'awakened.'"
--Shakyamuni Buddha, Dona Sutra
Mysteriously, we're not born enlightened. We're born with a baby's mind that gets angry, frustrated, and jealous. As we grow up, our minds expand, we learn a lot, and we seem to grow out of that behavior. However, the baby-mind is still in there, at the core, and all the new layers are simply installed on top: the child-mind, the teenage mind, the college student mind, the young adult mind, the older adult mind...
The new layers simply modify the baby impulses in order to make them look more polite or professional. When something annoying happens, the baby-mind still throws tantrums deep down. Those tantrums are now too deeply buried to be experienced or expressed directly, so they work their way up through the hierarchies of the brain and eventually come out in the form of a plan, an argument, or some kind of violence.
Unfortunately, many times these infantile emotions are so out of touch with reality that your mind can lead you to self-destructive behavior. People can turn to drugs to make themselves feel better, but they actually make their problems worse. People go to war so they can exercise their aggression, but they come back traumatized or dead. Even smart people make dumb decisions based on deeply buried emotions.
Bridging this gap between our rational understanding of reality and our irrational emotional impulses is enlightenment. When someone is enlightened, they are shining the "light" of their conscious attention into the dark corners of their mind. In one sense, this invites the inner baby out of the darkness of its own delusions and teaches it to respond appropriately to reality. In another sense, this dissolves the inner baby. Once you see that the inner baby is not needed, you stop reinforcing the bad habits and those neural pathways can eventually restructure.
The same thing can happen to all the other layers of the mind. By peering into the roots of your teen angst, your college-mind ambition, and your adult greed, you can see how irrational, self-destructive impulses start and repeat. The end goal is to foster communication between all these parts of your mind--the emotional and the rational--so that they can work together. When this happens, the mind becomes unified. A unified mind is very powerful because it is no longer wasting energy on internal conflicts.
Prior to this unification, the emotional mind exists in a dark, murky fantasy world. When it "wakes up" to reality, that is--in a practical, psychological sense--enlightenment. This may not be the mystical, exalted enlightenment of the Buddha, but it is something meaningful. At least, it is a step toward a better way of life.