the.com/problem
A locked door that hasn't yet met the right key, or the right hammer.
means A situation that demands a solution because something is wrong, stuck, or unresolved.
from From Greek problema, literally a thing thrown forward — an obstacle tossed in your path to be picked up and wrestled with.
Math senseA million dollars awaits each unsolved Millennium Prize problem.
Hidden flipEvery problem is an opportunity wearing inconvenient clothes.
Greek rootPro plus ballein: to throw before you.