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Phrase(s): For want of a nail the shoe was lost; for want of a shoe the horse was lost; and for want of a horse the man was lost.
Prov. Overlooking small details can have disastrous consequences. (You can quote any of the sentences in this proverb by themselves.) • Jill: I don’t think we need to check our bicycle tires before we go for our ride. Jane: I disagree. For want of a nail the shoe was lost. • Before we began the hike into the mountains, we checked our equipment painstakingly, remembering that for want of a horse the man was lost.
McGrawhill's American Idioms And Phrasal Verbs