the tip of the iceberg

The tip of the iceberg is when a small minute detail, part, or aspect of something is largely hidden or when the truth about something is only a small detail of it, and should not be counted as the main problem. In the case of an iceberg, the size and possible damage of the entire iceberg is what makes it so dangerous, not the tip of the iceberg which on its own is bad, but not compared to the rest of the iceberg.