This statement derives from the general relativity theory published by Albert Einstein in 1915. It refers about the event in which an accelerated body crosses the spacetime boundary of a black
hole known as the "event horizon". Beyond this boundary or "point of no return" the gravitational pull becomes so great as to make escape
impossible and thus "you'll
never go back".
"If a black
hole is an oyster then the singularity is the
pearl inside. The gravity is so strong it’s always hidden in darkness, beyond the horizon. That’s why we call it a black
hole, once you go black you'll never go back."