"The really explicit phrase is doors of perception."

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We pursue modernity in her incessant metamorphoses yet we never manage to trap her. She always escapes: each encounter ends in flight. We embrace her and she disappears immediately: it was just a little air. It is the instant, that bird that is everywhere and nowhere. We want to trap it alive but it flaps its wings and vanishes in the form of a handful of syllables. We are left empty-handed. Then the doors of perception open slightly and the other time appears, the real one we were searching for without knowing it: the present, the presence.

— Octavio Paz