Only through unwavering perseverance can contemplative practice (vipaśyanā-caryā) reach natural fruition.

Lantian's Breath Observation Diary: In the evening I sat down and did ten minutes of active deep breathing. Before finishing the deep breathing, I gradually developed a sensation of qi. Afterwards, I observed the breathing at the nose. On the fourth inhalation, I felt the qi mechanism in the dantian stir, and the abdominal muscles began to twitch irregularly. As I slowly inhaled and exhaled, the twitching of the abdominal muscles increased. After one inhalation, I paused and waited in stillness; the abdominal muscles began to contract rhythmically, causing the abdomen to continue expanding, while also drawing the chest and flanks outward. The airflow kept being drawn in through the nostrils until the abdominal muscles felt swollen, and the exhalation came out naturally. In this way I entered deep breathing, while my attention remained on the breath at the root of the nose. After about ten minutes, near the end of one inhalation, the muscles of the lower abdomen began to contract, and I felt the airflow surge downward again, as if reaching the very bottom. The chest and abdomen were like an air box, with the airflow entering and leaving. This continued until the end of the meditation session. 

During today's deep breathing, the abdomen was much hotter than before. When inhaling, it filled with air; when exhaling, I felt the muscles of the abdominal cavity coming together, and the abdomen felt very comfortable. During this time there were very few wandering thoughts; unless I deliberately thought about something, no other stray thoughts flashed through my mind. After the meditation ended, I continued sitting on the bed, breathing slowly. At that moment, fellow practitioners in the group chat started a conversation about the feelings during meditation. After talking for a while, I could no longer speak, because while speaking, due to the momentum, the dantian was still strongly inhaling and exhaling, making it impossible to continue talking. So I rested. 

Assessment: If you persist in observing the breath every day, your meditative concentration (samādhi) will get better and better, the mind will become increasingly refined and focused, and your observation will become increasingly detailed; and the more detailed the observation, the more focused the mind becomes, and the better the samādhi—this is a virtuous cycle. However, once the practice becomes fully mature, there will be no new changes in the phenomena observed, and it will feel as if one's cultivation is making no progress and has stagnated. At this point, divergence will occur: some people will feel bored and that it is meaningless, and gradually a mentality of weariness and regression will arise. In fact, as long as you persist, your practice is constantly improving; in the early stages it is quite obvious, while in the later stages it is merely not obvious. It is like being in shallow water, where everything one does is clearly revealed; but once one walks into deep water, everything one does is no longer apparent. 

Once you understand this principle, you must overcome this feeling of boredom and not give up halfway. The better the practice, the less obvious it becomes. Do not be concerned with the apparent stagnation—it is merely a moment that tests a person's patience. Only those who have patience and unyielding perseverance can reach the summit.