Prognostics do not always prove prophecies—at least the wisest prophets make sure of the event first.

Walpole’s epigram turns on a skeptical distinction between forecasting and foretelling. “Prognostics” suggests signs, probabilities, or learned predictions; “prophecies” implies authoritative certainty about the future. The punchline—“the wisest prophets make sure of the event first”—satirizes those who pose as seers but only “predict” what has already happened or is safely inevitable. It is a jab at hindsight wisdom, political punditry, and self-protective rhetoric: the cleverest avoid being wrong by waiting until outcomes are known. The remark fits Walpole’s broader wit as a letter-writer and commentator on public affairs, where irony often exposes vanity and pretension in claims to insight.