(classifier used before a noun that has no specific classifier) / (bound form) individual
个
=
丨
+
人
:
Mnemonic symbol: Neanderthal Man (人). Neanderthal Man (人) needs to use the elevator's bathroom (e4) but it's occupied by Guy Fawkes (g), and there's only space for one individual (个). Impatiently Neanderthal Man knocks on the door using his dinosaur bone (丨).