握不住的沙干脆扬了他

It's used as a metaphor for when things cannot be retained or controlled (like grains of sand slipping through your fingers). So this username suggests 'if something can't be grasped onto anymore, just let go', indicating that sometimes one might as well just let go of what they cannot keep instead of clinging on to futile things. This implies giving up rather than holding too tight and getting hurt by losing control or possession.