Einstein isn't simply praising flexibility—he's redefining intelligence itself as a dynamic process rather than a fixed possession. Most of us think of intelligence as the sum of what we already know, but he's saying the real mark of a keen mind is recognizing when old thinking has become obsolete and having the courage to abandon it. A scientist who clings to a disproven theory, or a business leader who refuses to adapt their strategy despite market evidence, reveals not stability but intellectual stagnation. The sting in this observation lies in how it exposes that stubborn certainty—the thing many mistake for wisdom—is actually intelligence's opposite.