Enlightenment isn’t an occurrence any more than falling is. It's a procession, a gradual unfolding of personal and spiritual ability that happens over lifetimes. Each place and time you find yourself in, you’re a little better, a little more conscious, a little wiser.
With each life event, an old part of you dies and a new self is born from the ashes. This new self carries with it a tiny amount of extra will. This isn’t the “willpower” you’re used to, it’s not a conscious thing at all, though you can feel it if you meditate enough on it. The whole being is upgraded, a tiny amount. The main reason you can’t see it is because your mind is tuned to see big things.
By the time you reach awakening, you’ve already led many lifetimes in which you were spiritual but it never quite clicked for you. By the time you become enlightened, you’ve already lived countless lifetimes where you became awakened. Before your first spiritual experience, you lived countless lifetimes as a rational, decent person. Everybody evolves and everyone has their place on the map.
Enlightenment as non-duality can be more or less felt in a given moment. Your brain is all just neurons and electricity in the end, and that is what determines your momentary experiences. It’s your capacity for pushing yourself to constantly evolve each and every moment, to have the ability to decide, each and every moment, to discard your self and allow a new one to arise, that forms the ground upon which an enlightened brain, mind, and person can sprout.