Often used in the military, especially basic training. Used to describe an individual who suffers from the inability to properly "man the fuck up" and get through a difficult or trying task.
Drill Sergeant - "Alright you little poster boys for abortion, get your gear and get outside right fucking now. And if I hear a single one of you suffering from THS I will personally beat you until your tiny little fucking heart stops."
"Did you see George cry his way out of finishing work today. Said his head hurt to much to continue on. I'm tired of him never finishing a single thing."
"That prick is a chronic case of THS (Tiny Heart Syndrome)."