Plot is a vehicle. It is the method by which you present your story.
Plot is a purposeful sequence of events. In a well-plotted story, those events connect logically, culminating in a specific goal, or climax.
“Life is an unceasing sequence of individual actions.”
Said Ludwig von Mises.
That is true. Plot is similar, but plot is selective in the actions presented. And the author is the selector.
Plot is purpose — and for this reason plot requires adversity and obstruction. It requires struggles and obstacles of some sort. Why does plot require this? Because it is only by means of such things that characters can be presented and developed interestingly.
Plot is drama, and drama is what holds the reader’s interest. It is in turn only by means of such things as characters that a theme — which is the essence of a story’s meaning — can be portrayed.
As the late Kurt Vonnegut said:
“I guarantee you that no modern story scheme, even plotlessness, will give a reader genuine satisfaction, unless one of those old fashioned plots is smuggled in somewhere.”
Plot is not action alone. It is not random events. Neither is it a series of conversations (even if those conversations are in and of themselves interesting), and it is not a catalog of day-to-day or minute-by-minute activities.
Novels are by definition about human action. If, therefore, the subject of the story isn’t dramatized in terms of action, it is not a successful story.
Within this framework, there are degrees of plot-versus-plotlessness. Thus, of a story that has a sequence of actions that aren’t motivated by purposeful action but rather by accidents, it is appropriate to call this a plotless story. But of a story that has a sequence of events which does progress purposely, or even semi-purposely, and yet which is resolved by pure chance — or if there are actions unrelated to the storyline — it is likewise appropriate to call this a plotted but poorly plotted story.
To dismiss plot because it is invented, or to describe plot as an unnecessary contrivance, as many do, is like dismissing chess rules as an unnecessary contrivance and yet trying to play chess without them.
Plots are invented because humans need to see human life in compendiated, encapsulated form. That, incidentally, is the function of art — all art — and that is why plots are the indispensable device of storytelling: because they encapsulate, via the writer’s selection of events, the human experience.