失之毫厘，差之千里
shī​zhī​háo​lí​chà​zhī​qiān​lǐ

a tiny lapse can lead to a huge mistake

  1. 失 shī nounverb
    mistake
    (bound form) a mistake; a fault; a defect; a mishap
  2. 之 zhī particle
    [nominalizer]
    Used between a subject and a verb to turn the phrase into a noun-like unit.
  3. 毫厘 毫釐 háo​lí
    an iota
    the least bit; an extremely small amount
  4. ， chà
    non-Chinese
  5. 差 chā noun
    difference
    difference; discrepancy; the result of a subtraction in mathematics
  6. 之 zhī particle
    [nominalizer]
    Used between a subject and a verb to turn the phrase into a noun-like unit.
  7. 千里 qiān​lǐ
    a thousand li
    one thousand 里 lǐ; approximately 500 kilometers; used metaphorically to mean a very long distance