Draw the letter U on the road with your car: go down one side, curve round the bottom, come back up the other side. You are now facing exactly where you came from. That shape is the whole word. What matters in it is not the turning but the ending — you end up opposite. So when the word leaves the road, it keeps that: a leader who said one thing in May and the opposite in June has driven the same U, only on paper.
用車子在路面上畫一個字母 U：往下走一邊，在底部繞過去，再從另一邊開回來。現在你正對著剛才來的方向。這個形狀就是整個詞。重點不在「轉」，而在「轉完之後朝哪裡」——你面對的是完全相反的方向。所以這個詞離開馬路之後，帶走的也是這一點：五月講一套、六月講相反的一套，那個人畫的是同一個 U，只是畫在紙上。
From the word’s history
From U + turn, named after the similarity to the shape of the letter U.
來源資料記載這個詞就是 U 加 turn，因為這樣轉出來的路線形狀像字母 U。字形本身就解釋了它的核心：彎到底，最後朝向相反。
Wiktionary entry for U-turn (etymology: From U + turn, from the similarity to the shape of the letter U), supplied in the evidence packet
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