For Aristotle, the play should approximate or copy human and/or divine actions in mimesis—actions made intelligible and believable by laying them out in an orderly sequence. The implications of the actions should be serious problems that both absorb the audience members’ attention and instruct them according to some moral principle. The protagonist’s downfall, according to his or her tragic flaw, would be a strong element of communicating that principle.
In order to keep the audience following along and to create that sense of plausibility, the plot needed to be arranged in a logical way. However, the emotional identification of the audience with the hero’s downfall must also bring about catharsis, or release. Therefore, the plot structure must build to a dramatic high-point, the climax, that would capture the audience. Each event in that linear sequence need not be obvious, as in easily anticipated, but each should make sense once it is revealed and there should only be as many as can easily be remembered. The climax would logically be followed by the resolution, as the ends are all neatly tied up, including the fate of each character (those who do not die).