Insurmountable means too great an obstacle to get past. An insurmountable problem, seemed insurmountable, not insurmountable.
It is used far more often than it is true, which is why not insurmountable is such a useful reply. It belongs to difficulties rather than to walls, since the literal sense has faded entirely.
1adjectiveinsurmountableToo great an obstacle to get past.
“With no money and no road, building the school seemed an insurmountable task.”
insurmountable is a quality.
From in- + surmountable.
Etymology from Wiktionary, CC BY-SA