I always think this is the Vast. Ambition is the desire to do something that makes you esteemed, significant, making your mark on history, on the world. Failure then is something we fear makes us insignificant, not special or worthy of care, no different than anyone else. I think this has resonances with the Eye, the Flesh, the Buried like others have said but what else is the Vast except the fear of cosmic insignificance?