Most of the things worth doing in the world had been declared impossible before they were done.

The remark frames “impossible” as a social verdict rather than an objective limit. Brandeis’s point is that many achievements—legal reforms, technological advances, expansions of rights—begin as proposals that conventional wisdom dismisses. The quote encourages persistence and moral courage: if worthwhile work is routinely branded unrealistic, then opposition and skepticism are not reliable indicators of futility. In a Brandeisian key, it also hints at democratic experimentation: progress often comes from challenging entrenched interests and inherited assumptions, and history repeatedly shows that today’s “impossibilities” can become tomorrow’s settled facts.