It always seems impossible until it's done.

The line expresses a pragmatic optimism about human effort: daunting tasks often feel unattainable while they are still abstract, untested, or opposed by entrenched obstacles. Only after sustained work—planning, persistence, collective action—does the “impossible” reveal itself as merely difficult. The aphorism resonates with Mandela’s public association with long struggles (especially the anti-apartheid movement), which makes it rhetorically powerful even when detached from a specific speech. Its appeal lies in reframing fear and uncertainty as temporary perceptions rather than objective limits, encouraging perseverance until results make the former impossibility seem like an illusion.