About This Answer
A meditator back from retreat asks when to let go of a single object and let attention move to others, since on retreat awareness of the whole body began dissolving and attention moved quickly from place to place. Ajahn Dtun answers that if the aim is concentration, one stays with the chosen object, such as the breath, and keeps bringing the mind back; letting it wander spreads mindfulness thin, whereas the purpose is to make the mind one-pointed.
Once the mind is one-pointed and the aim is wisdom, it is right to investigate the body. This means probing deeply rather than noticing surface sensations: breaking the body down into its parts or the four elements, or contemplating its unattractiveness, to see that it is impermanent and not self.
A follow-up asks how much seeing is enough to remove the defilements. He says one clear sight is rarely enough. The body must be contemplated again and again, resting when the mind needs rest. He compares it to eating a meal: one keeps taking mouthfuls until full, then puts the knife and fork down. When understanding matures, the mind lets go of attachment by itself.