<|im_start|>user
Why do we say tip of the iceberg?<|im_end|>
<|im_start|>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.<|im_end|>
