Stoic impressions matter because discernment begins not with certainty but with what appears, and the first discipline is refusing to confuse appearance with truth.
In Stoicism, an impression is what presents itself to the mind before judgment.
That includes what you see, hear, feel, remember, or imagine. The crucial point is that the impression is not yet truth. It is what appears.
This is why Stoicism maps so naturally onto the perception layer in the discernment model. Perception is the contact point with what seems present. But what seems present is not yet identical with what is.
Error begins when the mind treats the first appearance as final reality. A delay becomes rejection. A tone becomes hostility. A bodily reaction becomes proof. The Stoic discipline begins by reopening the gap between appearance and judgment.
This is not abstraction. It is the foundational move that makes all later discernment possible.