Every teacher stresses on the importance of regular and continuous practice of Reiki self healing for twenty-one days after attunement. There are several reasons for this.
Firstly, during these 21 days, a lot of cleansing takes place in your body. You must ensure you drink plenty of water and sleep sufficiently. Regular Reiki practice during these days helps remove the negativities accumulated by your body over your lifetime. Each chakra takes roughly 3 days, hence the 21 days.
Secondly, your body is still new to the energy being channeled, and it takes 21 days for it to get adjusted to the new activity. From a psychological aspect too, it has been found that a person takes about 21 days to form a habit.
Most importantly, a lot of reiki students assume that since so much of stress has been laid only on the first 21 days, the days after that must not be important. Quite the contrary, you need to continue practicing Reiki everyday even after the 21-day period. During the 21 days, you must just ensure that you do not miss practice even once, and also remember that the more number you practice, the better the effect.