What is the origin of the idiom "tip of the iceberg" and when to use it?

The phrase "tip of the iceberg" comes from the literal idea of an iceberg, which is a massive piece of ice floating in the ocean. However, what is visible above the water's surface is just a small portion of the entire iceberg; the majority of it is hidden beneath the water. This concept was first popularized in the early 20th century to describe situations where only a small, visible part of a larger issue or problem is apparent.