The tip of the iceberg is the small visible part of a much bigger hidden problem. Just the tip of the iceberg, the tip of the iceberg only, this is the tip of the iceberg.
About nine tenths of an iceberg sits below the water, which is exactly what the phrase relies on. It is used in reporting to say the known cases are a fraction of the real number.
1phrasetip of the icebergThe small visible part of a much bigger hidden problem.
“The few complaints we've received are only the tip of the iceberg; most unhappy customers never write.”
tip of the iceberg is a part.
From the fact that roughly nine tenths of a floating iceberg lies below the surface.
From the fact that floating icebergs typically have about nine-tenths of their volume below the surface of the water. Early 20th-century uses of the term are believed to have been influenced by the sinking of the R.M.S. Titanic on April 15, 1912 after it struck an iceberg.
Etymology from Wiktionary, CC BY-SA