The mechanism is simple. When you breathe in mindfully, "Breathing in, I know I'm breathing in", I focus my attention on my in-breath and stop the thinking. I just become aware of my in-breath. My in-breath is the only object of my mind. I focus all my attention on my in-breath. I am concentrated. I allowed mindfulness and concentration to be present. And suddenly, I discover I'm alive. That is insight. It's very clear. When you breathe in mindfully, you know that you are alive. Because someone who is already dead does not breathe in anymore.
The key is to stop thinking, or to stop mind. When we (ego) stop thinking, awareness (true self) revives automatically. This is the self-transformation, or the Self-realization in yoga. Awareness can touch the wonders of life, so feel joyful and happy. This is the art of happiness. Thay calls this state as the part-time Buddha.
However, if we have not thrown away all notions, we will resume thinking and return to ego. Therefore, the extinction of all notions is essential in order to attain full enlightenment. And for the extinction of all notions, we need to be convinced that all notions are wrong. That's why we need to understand the ultimate truth. Once we attain full enlightenment, we will never resume thinking and return to ego. Thay calls this state as the full-time Buddha.
During the deep sleep state, everyone is awareness because we don't think. And during the awakening state and the dreaming state, the fully-enlightened person can stay awareness without thinking. So, the fully-enlightened person can attain insights 24 hours a day as awareness.