One way to hold this word is to stand at the door itself: several panels joined to a pole in the middle, turning all day. Nobody opens it and nobody closes it. You push, it carries you round, and you come out on the other side. Because it never stops, one person can be going in at the very moment another is coming out — and if you do not step off, the same door brings you back to where you started. Every other use of the phrase borrows one part of that picture: the steady stream of people, or the coming back round.
這個詞可以想成一扇一直在轉的門：幾片門板連在中間的軸上，沒有人去開它，也沒有人去關它。你推一下，它就帶著你繞過去，你從另一邊走出來。因為它不會停，所以有人進、有人出可以同時發生；而如果你沒有在出口踏出去，同一扇門就會把你帶回原來的位置。後面幾個比喻用法，都是各拿走這個畫面的一部分——有的拿「人流一直換」，有的拿「又繞回來」。
登入就可以看每一支怎麼連回核心畫面。