Two kinds of things have opposite characteristics in nature, size, appearance and so on. When people recognize one thing, they will think of another thing from the opposite. This kind of association is called contrastive association.
Su Shi's nostalgia for Nujiao Chibi and nostalgia: the river flows eastward, and the surging waves sweep away all the heroes of the ages. To the west of the old camp, people say that is Chibi where Zhou Yu fought fiercely during the three Kingdoms period uses contrastive association according to the above definition.