Maybe the difference between the two boys can best be described in this way. If Aaron should come upon an anthill in a little clearing in the brush, he would lie on his stomach and watch the complications of the ant life—he would see some of them bringing food in the ant roads and others carrying the white eggs.  He would see how two members of the hill on meeting put their antenna together and talked. For hours, he would lie absorbed in the economy of the ground.

If, on the other hand, Cal came upon the same anthill, he would kick it to pieces and watch while the frantic ants took care of their disaster. Aaron was content to be part of his world, but Cal must change it.

From “East of Eden” by John Steinbeck

This is a beautiful prose by John Steinbeck and one of the best analogies ever written to distinguish between two different personalities:  Cal, the figure of Cain in this novel and Aaron, that of Abel.  See the elegant use of ‘should.’—”should come upon an anthill”—instead of the past tense or past perfect in the first if-clause. Notice the repetition of ‘I would see’ to enhance the power of the sentences and their impact on the reader.  His conclusion “Aaron was content to be part of his world, but Cal must change it” is absolutely magnificent.