. . . But I know a man who can.

The fragment “But I know a man who can” is typically used as a pivot from doubt to confidence: after listing what “can’t be done,” the speaker asserts that someone exists who can accomplish it. In anonymous or proverbial usage, it functions as a rebuke to defeatism and a reminder that limits are often social or psychological rather than absolute. The line also implies the power of exemplars—one capable person can reset a community’s sense of what is possible. Because the quotation is incomplete and lacks a stable attribution, its meaning depends heavily on the surrounding narrative (often a story about innovation, persistence, or an underestimated individual).