Some people do not know the difference between "mindfulness" and "concentration."

They concentrate on what they're doing, thinking that is being mindful. . . . We can concentrate on what we are doing, but if we are not mindful at the same time, with the ability to reflect on the moment, then if somebody interferes with our concentration, we may blow up, get carried away by anger at being frustrated.

If we are mindful, we are aware of the tendency to first concentrate and then to feel anger when something interferes with that concentration. With mindfulness we can concentrate when it is appropriate to do so and not concentrate when it is appropriate not to do so.

About Ajahn Robert Sumedho : 

Luang Por Ajahn Sumedho is the senior Western representative of the Thai forest tradition of Theravada Buddhism. He was abbot of Amaravati Buddhist Monastery just north of London from its consecration in 1984 until his retirement in 2010.

Luang Por Sumedho was born in Seattle,Washington. In 1966, he went to Thailand to practice meditation and not long afterwards, he went forth as a monk. He took dependence from Luang Por Chah and remained under his close guidance for ten years. In 1977, he accompanied Luang Por Chah to England, helping to establish Chithurst Monastery and later Amaravati, where he is currently abbot.

Source: Abhayagiri: General Essay's