I think sadness is grief’s little brother, popping up unannounced, at inopportune times, sometimes loud and ugly, sometimes whisper quiet.
Grief is stone, seemingly always there, strong, heavy, unmoving, wise. I suppose, like stone, it wears away slowly, its rock face getting smoother over time, changes happening slow enough to go unnoticed.
Sadness comes and goes, child-like in its fleeting nature. Alone, sadness is distinct from laughter, separate from joy. But they play together with grief.