Why do we say tip of the iceberg?
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.
Below is an instruction that describes a task, paired with an input that provides further context. Write a response that appropriately completes the request.
### Instruction: Why do we say tip of the iceberg?
### Input: 
### Response: 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.