an error of the breadth of a single hair can lead you far astray—a small discrepancy leads to a great error
失之毫厘，谬以千里
an error as small as a single hair can lead you a thousand li off course(or astrag);a small discrepancy can lead to great blunder
失之毫厘，谬以千里shī zhī háo lí,miù yǐ qiān lǐ
只稍微差一点，就会造成非常大的错误。A small discrepancy leads to a great error. A miss is as good as a mile.