One picture carries the whole word: something gives way when you press it, and comes back. Soft leather folding under your thumb. A green bamboo stem leaning in the wind. A warm back curling forward. It bends instead of resisting, and — this is the part that matters — it does not crack.
The packet traces supple through Old French souple to Latin supplex, the word for someone kneeling or submissive, and splits it into sub- plus plico (to bend) — while marking the formation as uncertain. So a bending body sits in the oldest layer of the word, and the yielding sense is not a later invention but part of the same root.
字源可以追到古法文 souple，再往前是拉丁文 supplex——跪下、低頭順從的樣子；來源把它拆成 sub-（在下）加 plicō（彎），同時註明這個組成並不確定。所以「彎下去」這個動作，從最早那一層就在字裡面。順從的意思也不是後來才加上去的，它和身體的彎是同一個根。
Wiktionary entry supplied in the evidence packet (source_ref kaikki:3f6f69a190036ae4:931829258); the source itself marks the formation uncertain.
From the picture
彎得下去的心思與做法
從看得見的彎，走到看不見的彎：想法肯改、計畫肯調、意志肯讓。這是一條教學上的連結，不是在說歷史上先有哪一個。
adjective · C2
Used about a mind, a plan, a system or a person's will: ready to change or give way instead of staying fixed. It can mean quick to adapt, and it can mean willing to yield to what someone else wants.
肯變通的；肯順從的
adjective · C1
Leather, skin, wood and similar material that is supple is soft enough to bend and fold easily, without cracking or breaking.
柔韌；軟而好彎
adjective · C1
Able to bend and move easily and smoothly, with no stiffness — used about a person, or about a part of the body such as the back, hips or fingers.
柔軟靈活