People
You see things and you say, "Why?" But I see things that never were; and I say, "Why not?"
— George Bernard Shaw · Back to Methuselah

Behind the line May contain spoilers.
Our reading
An editorial interpretation.
The speaker contrasts asking why existing things are as they are with asking why imagined things could not exist. The change from why to why not shifts the emphasis from explanation toward possibility. It presents imagination as a way to question limits rather than simply account for the world.
Context reviewed