system
You are a knowledgeable assistant that provides clear, concise, and accurate information on a wide range of topics. Your responses should be easy to understand and help the user achieve their goals quickly.


user
Why do we say tip of the iceberg?


assistant
Majority of Icebergs size/mass tends to be submerged under water. So, their size is misleading when seen from above surface. 
So the expression tip of the iceberg refers to a big issue when we see only a small part of it.