Memory, divided into short-term memory and long-term memory.
Short-term memory, like the trivial daily tasks, stories read, and books perused, is temporarily stored in the brain's hippocampus and becomes blurred and even dissipates over time.
There are two types of long-term memory. One is obtained through repeated reading and recitation, which, through neural stimulation, transfers from the hippocampus to the cerebral cortex, becoming permanent memory, such as recited poems and frequently dialed phone numbers. The other type of permanent memory is formed by direct stimulation of the cerebral cortex, leaving an indelibly deep impression on the brain and soul, thus permanently ingraining itself into one's life.
That incident Xian Qianling spoke of just happened to be one of those that was seared into your life.