the.com/tip of the iceberg

means A small, visible part of a problem that hints at a much larger, mostly hidden issue beneath it.

from Literal icebergs famously show only about a tenth of their mass above water, the rest submerged and invisible — a fact sailors and whalers knew firsthand from dangerous encounters. The phrase moved into figurative English in the early 20th century, with the Titanic disaster in 1912 likely cementing the image in public imagination, though the metaphor itself probably built up gradually in maritime and journalistic usage rather than being coined in one stroke.