the "7219 rule" means that if you repeat something seven times, you will know it and remember it. If you repeat it 21 times, you will form a habit. If you repeat it 9 times, you will solidify it and form a stable habit that is difficult to get rid of. When developing a good behavior and habit, we also follow the 7219 rule: the formation of behavior habits is roughly divided into three stages: the first stage: about 1-7 days. This stage is "deliberate and unnatural", so you need to remind yourself very deliberately that it is very uncomfortable and painful, and you should be determined at this stage. The second stage: about 7-21 days. This stage is "deliberate and natural", but it still needs conscious control. If you don't deliberately rebound, you should be determined and patient at this stage. The third stage: about 21-9 days, this stage is "casual and natural", without conscious control. This habit and character have been formed, but they still need to be maintained. At this stage, we should have determination, patience and perseverance. As long as it lasts for 9 days, we will develop good habits of treating children for so long.