Gus Grissom taught NASA a hard lesson: “You can hurt yourself in the ocean”
Respectfully, it's an interesting thought exercise to speculate what might have happened to NASA’s Moon program had Grissom died at the end of his Mercury flight instead of keeping his wits about himself. His flight came eight weeks after President Kennedy had told Congress he intended for America to send a human to the Moon "before this decade is out."
Grissom found salvation from his Mercury woes when NASA began working on the new Gemini spacecraft line that would allow the space agency to take critical steps toward a lunar program, including orbital rendezvous. The Gemini spacecraft was larger than Mercury, could accommodate two astronauts, and allowed for spacewalks.
“I felt pretty strongly that the ones who had been with the program the longest deserved first crack at the goodies,” Slayton wrote. “Had Gus been alive, as a Mercury astronaut he would have taken the step.” And so it was exactly eight years after Grissom's near-death in the water, less a single day, that Neil Armstrong and Buzz Aldrin landed on the Moon. Their giant leap for mankind would not have been possible but for the critical first steps of almost forgotten heroes like Grissom.