This trophy is called "Worrywart
" and it requires the user to heal their party when they don't need healing.Please note
: Najinceil has left a comment stating they have unlocked Worrywart upon Erik joining the party. I personally unlocked this after Rab and Jade joined my party. So, thanks to Najinceil, it is known that once you actually have a party of one (1), it's unlockable. :D
Travel to a Campsite and select the Rest option to fully heal. Once waking up and returning to the map, press the Triangle Button and then the Square Button. This will attempt to heal your healthy party and unlock the trophy when dismissing the dialog window.