行百里者半九十

xíngbǎilǐzhěbànjiǔshí
  1. lit. ninety li is merely a half of a hundred li journey (idiom)
  2. fig. the closer one is to completing a task, the tougher it gets
  3. a task is not done until it's done

CEDICT

Things become more difficult when we approach closer to success

Wiktionary

Entry Composition

1 行 xíng
  1. (bound form) to walk; to go; to travel
  2. (literary) trip; journey; visit
  3. (bound form) temporary; makeshift
  4. (bound form) current; in circulation
  5. (bound form) to do; to perform
  6. capable; competent
  7. all right; OK!; will do
  8. behavior; conduct (Taiwan pr. xìng)
  9. (literary) about to; soon
=2 百里 Bǎilǐ two-character surname Baili
=2 百里 bǎilǐ
  1. (literally) a hundred li (an ancient Chinese length unit)
  2. (literary, figurative) long distance
  3. a hundred li (an ancient Chinese length unit)
  4. a surname
  5. long distance
3 者 zhě
  1. (after a verb or adjective) one who (is) ...
  2. (after a noun) person involved in ...
  3. -er
  4. -ist
  5. (used after a number or 后 hòu or 前 qián to refer to sth mentioned previously)
  6. (used after a term, to mark a pause before defining the term)
  7. (old) (used at the end of a command)
  8. (old) this
4 半 bàn
  1. half
  2. semi-
  3. incomplete
  4. (after a number) and a half
5 九十 jiǔshí ninety