The tip of the iceberg.
Just a small part of a bigger issue.
The tip of the iceberg" is used to indicate that what is visible or known is only a very small amount compared to the larger, hidden aspect. Just like an iceberg, where only a fraction is seen above the water's surface, this iditem invites deeper investigation to understand the full scope of an issue or problem.
Example Sentences
That mistake was just the tip of the iceberg.
It means that mistake is only a small part of a larger issue.
The issue you mentioned is merely the tip of the iceberg.
It suggests the mentioned issue is only a small, visible part of a more significant problem.
When the company reported financial losses, they revealed just the tip of the iceberg since the overall financial health was far worse.
It indicates the financial issue reported is just a small part of a much bigger financial problem.