It is not possible that there should not be stumbles, failures, etc. in the work of self-purification and change, but to feel upset or remorseful over them is harmful rather than helpful; it easily brings depression, and depression brings clouding of the mind and weakness. To observe calmly the wrong movement and its nature (here it was the tongue that was at fault and the tongue is always an easily erring member) and to set it right inwardly is always the best way. Calm, especially when the true spiritual calm of the Self is there, is the thing that must always be preserved; with that everything else can be done in time and with the least trouble.
Ref: Letters on Yoga – IV