What is the rarest LEGO set in history?

Hi everyone! I have a question that always creates a lot of debate among LEGO fans. In your opinion, what is the rarest LEGO set ever made? I’m talking specifically about official LEGO sets to build, not custom MOCs, not single prototype pieces, and not just rare minifigures by themselves. Things like limited editions, employee-only sets, tour-exclusive sets, or extremely low-production runs. I’ve heard people say that the LEGO 4000001 might be the rarest LEGO set ever made. Is that actually...