One way to hold gatekeeper: a long wall with exactly one opening in it, and one person sitting beside that opening. The wall does the real work of keeping people out; the person only has to sit there and say yes or no. That is the whole idea. Because there is no other way in, a small job at a narrow place turns into real power over everyone waiting outside.
gatekeeper 可以想成這樣一個畫面：一道很長的牆，上面只有一個開口，開口旁邊坐著一個人。真正擋住大家的是牆；那個人只要坐在那裡說可以或不可以。整個字的意思就在這裡。因為沒有別條路可以進去，一份看起來很小的工作，就變成了對門外所有人的實際權力。這道牆後來常常是看不見的。
From the word’s history
Wiktionary gives the word as gate + keeper — literally the person who keeps (looks after) the gate. Both halves are still visible: the gate is the one narrow way in, and keeping it means deciding what happens at it.
Wiktionary 記這個字就是 gate（門）加 keeper（看守的人），字面上是「顧那道門的人」。兩半到今天都還看得見：gate 是唯一的窄口，keep 是在那個口上做決定。
Wiktionary, "gatekeeper"
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