“The tip of the iceberg” refers to the reality that the majority of an iceberg lies below the surface. This is impressive when you consider how big some of them are above surface. It is estimated that roughly 7/8 of the iceberg is below the surface and not immediately visible. In the same way, our character is more important than that small part everyone can see “above the surface” (https://www.nationalgeographic.org/encyclopedia/iceberg/).