What is the reason behind the vast difference between the kid (young goat) and an adult Goat?

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I've done some personal study / observation on the behavioural pattern of most Animals, cause there's a lot to learn from them.

And funny enough, one Animal I've come to realise how awesome, positively vibrant, cheerful, fun and very worthy to emulate is the kid (the young goat).

But the adult Goat is nothing to write home about, save the meat delicacy, gotten from it.

People have been addressed as:

• A Lion,
• Dog,
• Cat,
• Bull,
• Monkey,
• Sheep / Lamb etc.

But never a Goat (except as an acronym).

In fact, calling someone a Goat is a lambasted insult to the person.

All because the Goat is one of the dumbest domesticated Animal ever.

But isn't it ironic that Children are also addressed as 'Kids' - derived from the Young Goat, because of its behavioural pattern which is harmonious with some of the qualities as of a Child.

So the question is;

What is the reason behind the vast difference between the kid (young goat) and an adult Goat?
(based on their behavioural pattern)?.