常 hangs a cloth 巾 under 尚: originally a long banner or lower garment — something always worn, always flying. From 'constant garment' to 'constant' itself: the unchanging, the usual.
常 sets life's baseline: 常常 (often), 非常 (extremely — 'beyond the constant'), 正常 (normal), 平常 (ordinary days). Chinese philosophy prizes 常 — the Dao De Jing opens by warning that the Dao that can be told is not the 常道, the constant Way. From Laozi to 我常常迟到 ('I'm often late'), the same character holds the ordinary together.
The banner 巾 that never comes down — CONSTANT, OFTEN.
非常 'not-ordinary' = extremely: Chinese intensifies by declaring something outside the constant.