About This Answer
The question is whether, when mindfulness is too weak to let something go, one should return to the meditation object. Ajahn Dtun says the answer is in the question. Moral virtue and concentration give rise to strong mindfulness, which can see thoughts, moods, greed and anger as they arise. Weak mindfulness cannot simply observe; it goes into the emotions and follows them.
He compares this to the body: to make it strong we exercise or lift weights. To strengthen the mind we develop concentration, which builds the mindfulness that can separate the mind from what arises and let it go.
So when mindfulness cannot reflect on and release what arises, that is the sign to return to the meditation object, even briefly, to re-establish concentration. Virtue alone without concentration leaves the mind without the strength or sharpness to cut through defilements.