Emerson suggests that people often judge an untested achievement to be impossible until someone demonstrates that it can be done. A successful example changes the available evidence: what previously seemed beyond reach becomes an established possibility. The quotation therefore draws attention to the way assumptions about limits are shaped by experience and precedent.

Within Experience, the statement reflects Emerson’s broader interest in perception and the provisional nature of judgement. Human beings frequently mistake the absence of a known example for proof that something cannot happen. Once success occurs, that judgement may change quickly. Emerson’s wording is deliberately sweeping and does not mean that every apparently impossible goal can eventually be achieved. Rather, it highlights how limited knowledge can make possibilities seem narrower than they are, and how concrete evidence can revise beliefs that once appeared certain.