丢三落四 (diū sān là sì) — forgetful, scatterbrained, absent-minded (especially about daily items)

Two or more meaningful parts placed together so that their meanings combine into a new one.

This origin belongs to the traditional form 丟; 丢 is its simplified writing.

The traditional form 丟 is made of 一 (one) and 去 (to go; to remove); the simplified 丢 is a later shorthand, so its shapes are not the original parts.

An abstract idea shown by a mark or a diagram rather than by a picture of an object.

三 is drawn as three parallel strokes, like 一 with one stroke and 二 with two.

Most characters — around four in five — are built this way: one part hints at the meaning, the other at the pronunciation.

落 pairs 艹 with 洛; 洛 gives the sound, and 艹 relates to the meaning.

A drawing of the thing itself, worn down over three thousand years into a few strokes.

The form 四 was drawn as a nose breathing out. It later came to be used for the word four.