Constantly Focusing Our Minds At Each Very Moment
Origin: Mid Agama Sutra No.98

One day, Buddha Shakyamuni told his deciples ," There are some skillful practitioners who had overcme disturbing thoughts and fear, pain and worries , and finally liberated themselves from attachments. The skillful dharma they practiced is called Focusing Your Mind In All Four Categories. Should a practitioner who has acquired the philosophy of emptiness, may he be in the past, present, or future, so long as he can detach himself from desires, eliminate all five impurities(Note 9), be free from his personal habitual patterns and obscurations of wisdom, and focus his mind single-pointedly in all four categories as well as taking the seven precepts, he is guaranteed to reach enlightenment in due course. What do I mean by Focusing Your Mind In All Four Categories? For example, to focus one's mind on what the body is engaging is called Focusing One's Mind On The Body; And focusing on one's mind on Dharma is called Focusing Ones's Mind on Buddha.

When monks walk, they should be aware they are walking; When they enter a house, they are fully conscious they are entering; When they sleep, they are actually performing sleep; When they wake up, they know they are waking up. Similarly, monks know how to concentrate their mind on whatever their body is engaging. To be able to adopt such single-pointed concentration momentarily without relax is named Observing The Body As Body Is. Furthermore, the mind should not escape from concentrating at every split second over whatever the body is engaging even at the time of bowing down, cleansing, getting dressed, begging for food, walking, sitting, sleeping, walking up, talking, and in silence. Monks should focus their minds on no talking when they focus on silence. Such is called Observing The Body As Body Is."

Buddha used many examples to explain to monks how to focus and what to focus to guide them. Buddha showed them how if one can concentrate single-pointely at all time,one leaves no gap for other thoughts to arise. For once you are focusing, the thought remains single-pointedly. There shouldn't be another thought. Because if it there is, it's not really full cncentration.