My research assistant and I haven't finished gathering bits and pieces relating to the compound I wanted to post today, so here's something last-minute.

大器晩成
tai ki ban sei
great vessel late make

That third character, 晩, almost always means "night" in modern Japanese (and Chinese, for all I know), but it means "late" here because the phrase comes from oldity old-old Chinese -- specifically, the Tao te Ching, chapter 40 or 41 depending on your editor.

The first half of the chapter is concerned with how various types of people react to information about the Tao, and the last half of which explores why the Tao is so difficult to understand, via a series of paradoxical analogies:

明道若昧、進道若退、夷道若纇。上徳若谷、廣徳若不足、建徳若偸。質真若渝、大白若辱、大方無隅。大器晩成、大音希声、大象無形。

Bright ways can seem dark; ways that go forward can seem to go backward; flat ways can seem bumpy. High virtue can seem lowly as a valley; boundless virtue can seem insufficient; healthy virtue can seem ailing. Innate truth can seem to change; great pureness can seem dirty, a square can seem cornerless. A great vessel is never quite finished. A great sound is never quite audible. A great image never quite has a shape.

(Note that if we used the modern meaning for 晩, we'd get "a great vessel is made overnight", which is exactly the opposite of what any self-respecting aphorism would want to say. Also note that 若, actually meaning "young", is here used to mean "is like" or "seems like" -- I think this is a phonetic thing.)

Anyway 大器晩成, in modern times, has come to mean something like "Rome wasn't built in a day". Unlike "Rome...", though, it can also refer to things that aren't a definite goal-oriented process, e.g. a friend who, although talented, remains unsuccessful.