Before tranquil dwelling was implemented during the summer months, monastics would wander about asking for alms in the sweltering heat, severe winter, and heavy rain. Such act brought about much criticism: “Even non-Buddhists wouldn’t go out in the rain in fear of stepping on insects. Why would monastics still choose to do this? Don’t they know that lives would be lost under their feet?”
Hearing this, Buddha implemented tranquil dwelling, a summer retreat where monastics would study devotedly within the doors of their monastery. This allowed them to continue their practice even during the months of the summer monsoon. By doing so, many achieve enlightenment at the end of the three month period. It made Buddha extremely happy. And so, the last day of the summer retreat came to be known as Buddhist Joy Day.