A plot-theme is a conflict in terms of action, complex enough to create a purposeful progression of events. If you recall that this last is the definition of plot, you will see that the plot-theme serves as the seed from which the tree has to grow. To test whether you have sufficient seed for a good tree, ask yourself: Is this the worst situation in which I can put my hero? If these are his values, is this the worst clash I can engineer between them?

If you have chosen the worst clash possible, and if the values are important, you have a good seed for a good plot structure.