Something described as hardscrabble is difficult and challenging. Adult success is a rare outcome for someone who lives through a hardscrabble childhood.
During an economic depression, many people's lives become hardscrabble, as they fight to find work, or are unable to pay their bills without working two or three jobs. This sense of struggling just to metaphorically keep your head above water captures the meaning of hardscrabble. It's an early 19th century US invention, first written in Lewis and Clark's journals, and referring to an imaginary place "where a livelihood may be obtained only under great hardship and difficulty."