There is no need to repeatedly contemplate the point about no-self in this practice. When the three practices are completed, simply reflect on whether the self exists or not. At that time, it will become quite clear: if dust particles do not exist and are empty, how can I exist? It is not possible. Once we have this profound realization of no-self, let the mind rest in this state. When the mind gets distracted, start the practice over again.
~Depicted from THE FOUR SEALS OF DHARMA - The Practice of No-Self
