Why is symbolic meaning different for each individual reader? What are some of the factors that influence what we understand in our reading?

Symbolism "will be determined to a large extent by how the individual reader engages the text. Every reader’s experience of every work is unique, largely because each person will emphasize various elements to differing degrees, and those differences will cause certain features of the text to become more or less pronounced. We bring an individual history to our reading, a mix of previous readings, to be sure, but also a history that includes, but is not limited to, educational attainment, gender, race, class, faith, social involvement, and philosophical inclination. These factors will inevitably influence what we understand in our reading, and nowhere is this individuality clearer than in the matter of symbolism."