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If your livelihood is poor, life becomes unbearable.
Literal
Standard-of-living [subject-が] bad [if-と] life [topic-は] hard-to-endure thing becomes.
Two patterns. (1) ~と is the conditional 'when/if' for general truths and inevitable consequences — 'whenever X, then Y.' (2) 耐え難い is a compound adjective from 耐える ('endure') + 難い ('hard to') — the suffix ~難い attaches to verb stems to form 'hard to X' adjectives: 読み難い (hard to read), 分かり難い (hard to understand), 言い難い (hard to say).