Question

The prettiest smiles hide the deepest secrets. The prettiest eyes have cried the most tears. And the kindest hearts have felt the most pain.

Answer 1

True - 100%

is that sadness is (uncountable) the state or emotion of being sad while pain is (countable|and|uncountable) an ache or bodily suffering,

As a verb pain is to hurt; to put to bodily uneasiness or anguish; to afflict with uneasy sensations of any degree of intensity; to torment; to torture.