In the book, Piggy is the voice of intelligence and reason. He is more mature than the other boys, and he is the smartest. For this reason, he has the best ideas.
However, Piggy is also an outsider. He is overweight, has asthma, and wears glasses. The other boys do not like how he is always yelling at them. For this reason, the other boys often ignore Piggy and his good ideas. Sadly, when they ignore Piggy, they are symbolically ignoring intelligence and reason.