The Blessed One said, "Suppose, monks, that a large crowd of people comes thronging together, saying, 'The beauty queen! The beauty queen!' And suppose that the beauty queen is highly accomplished at singing & dancing, so that an even greater crowd comes thronging, saying, 'The beauty queen is singing! The beauty queen is dancing!' Then a man comes along, desiring life & shrinking from death, desiring pleasure & abhorring pain. They say to him, 'Now look here, mister. You must take this bowl filled to the brim with oil and carry it on your head in between the great crowd & the beauty queen. A man with a raised sword will follow right behind you, and wherever you spill even a drop of oil, right there will he cut off your head.' Now what do you think, monks: Will that man, not paying attention to the bowl of oil, let himself get distracted outside?"
The monk replied: "No, lord."
This story tells us that we can easily get distracted by the outer disturbances. Our mind is so unsecure that we have to keep being aware of the surroundings until the state that we are not focus on what we are doing, our mind is wandering around and it is not staying at the present.
The bell of mindfulness is very good I feel, because in a day, most of the time our mind will not be at the moment, so when the bell rings, we calm down ourselves and bring our mind back to present, when our mind are at present, we will eventually be more aware of the surrounding, because our mind is clear.