The main reason the author wanted to climb Devils Thumb was because it had never been done.
I got it into my head to climb a mountain called the Devils Thumb. An intrusion of diorite sculpted by ancient glaciers into a peak of immense and spectacular proportions, the Thumb is especially imposing from the north: Its great north wall, which had never been climbed, rises sheer and clean for six thousand feet from the glacier at its base, twice the height of Yosemite’s El Capitan. I would go to Alaska, ski inland from the sea across thirty miles of glacial ice, and ascend this mighty nordwand. I decided, moreover, to do it alone.
Into the Wild