矜功不立

jīngōngbùlì
boasts a lot, but nothing comes of it (idiom)

CEDICT

自以为能立大功则功必不成。

重編國語辭典

Entry Composition

1 矜 jīn
  1. to boast
  2. to esteem
  3. to sympathize
2 功 gōng
  1. meritorious deed or service
  2. achievement
  3. result
  4. service
  5. accomplishment
  6. work (physics)
3 不 bù
  1. no; not so
  2. (bound form) not; un-
4 立 lì
  1. to stand
  2. to set up
  3. to establish
  4. to lay down
  5. to draw up
  6. at once
  7. immediately