Full Idea
Zeno said perceptions starts like an open hand; then the assent by our governing-principle is partly closing the hand; then full 'grasping' is like making a fist; and finally knowledge is grasping the fist with the other hand.
Gist of Idea
Perception an open hand, a fist is 'grasping', and holding that fist is knowledge
Source
report of Zeno (Citium) (fragments/reports [c.294 BCE]) by A.A. Long - Hellenistic Philosophy 4.3.1
A Reaction
[In Cicero, Acad 2.145] It sounds as if full knowledge requires meta-cognition - knowing that you know.
Book Reference
Long,A.A.: 'Hellenistic Philosophy' [Duckworth 1986], p.126