The answer is
Look at this magic ball of every day!
Eggs are everyday objects.
Knock it too hard and it runs away.
The egg breaks when hit and the contents "run" out.
Heat it up to stop its run in its track,
Cooking(heating) the egg solidifies the contents of the egg and makes it less runny.
But once it turned firm there's no going back.
You cannot uncook an egg.
It might become a new life, or nourish one old.
If the egg is fertilized, it becomes a chick, which is a new life. If not, it will be cooked to nourish a human that can eat solid foods.
Beneath its plate of armor lies a heart of gold.
The golden-colored yolk lies under the hard shell of the egg.