The document describes the process of how the mind can drift from the main subject of thinking. It provides 12 examples of hypothetical "drifts" that could occur when trying to understand the definition of "man" from a dictionary. Each drift moves further away from the original topic as associations and unrelated thoughts arise. By the end of the 12 drifts, the link to the first topic is completely lost. The document argues that training is needed to improve concentration and separate the functions of the mind to reduce drifting during serious thinking.