Even if a log stays ages in the water, it never becomes a crocodile.

What it means
Time spent among a people, or in a place, does not turn you into one of them, any more than a log left in the water becomes a crocodile. One telling gives it as a light-hearted answer to an outsider who is told they have "become a Fulani".
Fulani · West Africa
Source and context
From: Fulani, West Africa
Source: Fulani/Fulbe oral-tradition proverb, documented on the African Manners blog's Fulani proverbs page (africanmanners.wordpress.com, 2012), which gives it as a light-hearted retort to an outsider told "you have become a Fulani". Earlier recorded here as documented in Wikipedia's "Fulani proverbs"; that page does not contain it.

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