Boil the water and the scum will rise to the top.

What it means
Boiling does not create the scum; it brings to the surface what was already in the water. In the same way, a time of trial shows what was already in a person.
Amazigh · North Africa
Source and context
From: Amazigh, North Africa
Source: Berber/Amazigh oral-tradition proverb collections (special-dictionary.com, "26 Famous Berber Proverbs") — boiling water entry

The meaning given here is our own reading. Other interpretations exist.