Stand at the front door of a building and start counting upwards. The only question is whether the floor under your feet gets the number one, or whether it gets a name of its own and the counting starts above it. Both answers exist in English, so the same two words can point at two different floors.
可以想成站在大門口，抬頭開始數樓層。問題只有一個：腳下這一層算不算第一層？英文兩邊的答案不一樣，所以同一句 the first floor 會指到不同的樓。這個詞真正要教你的不是「幾樓」，而是「數字要從哪裡開始算」。知道這件事，整棟樓的號碼就都跟著對上了。