Picture something that one hand cannot manage — a full tray, a heavy sword, a ball coming in fast. A second hand has to come and join the first. That is the whole picture: not one, but two. English then does something quiet and useful with the word hand: it lets it stand for a person, as in all hands on deck or a hand at cards. Once hand can mean a person, counting to two counts people instead of fingers, and the same word can describe a saw that needs two workers.
The source entry records the word simply as two + handed, which matches the picture directly: 'to do with two hands'.
資料來源把這個字記成 two 加 handed，字面就是「跟兩隻手有關」，正好對上這個畫面。後面的分岔，只看 hand 被讀成手還是被讀成人。
Wiktionary entry supplied in this packet (etymology_text: 'From two + handed.')
Two branches
一個人的兩隻手
這一組把 hand 讀成真正的手：第二隻手過來幫忙第一隻，動作才做得成。
adjective · B1
Done with both hands at the same time, or needing both hands rather than one — either because the action itself takes two hands, or because the thing is too big or heavy to manage with one.
雙手並用的
兩個人各出一雙手
同一個「二」，數的東西換了。hand 在這裡讀成「人手」，所以 two-handed 變成要兩個人一起。
adjective · B2
A two-handed tool is one that two people use together, one at each end. The source evidence also shows the word used of a game or activity set up for exactly two people, such as a two-handed game of cards.
兩人合作的