Why do we say "The leopard can't changes its spots"?

Meaning:

The nature of things (usually referring to humans) is unchangeable - just as the leopard cannot change its spots, a person cannot change their nature.

Background:

And if you ask yourself,
'Why has this happened to me?"
it is because of your many sins
that your skirts have been torn off
and your body ill-treated.
Can the Ethiopian change his skin
or the leopard his spots?
Neither can you do good
who are accustomed to doing evil.


Jeremiah, 13.22-23, The NIV Bible.

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