The fickleness of fortune, the temporary nature of its generosity and interest in a man is what the monk wants to warn the others. And in his tale, the Monk reveals that one trait of Fortune is that she whimsically supports and then changes her mind about the person she favors without no warning.
In The Monk's Tale, we encounter seventeen stories that relate historical events. All of these stories have tragic commonalities. They tell the stories of heroes who, despite their success in life, all met sad ends. The monk blames these sad outcomes on Fortune. One of Fortune's traits is that she abandons people when they least expect it. This is one of the most common themes of Medieval tragedies.
This is more like an informal explanation of what the term <em>democracy</em> means. It mostly contains short and simple words, so it cannot be a formal definition or a dictionary definition. An extended definition is usually one or more paragraphs, so this text is too short to be an extended definition.