Fans of Star Trek long ago noted that anonymous security officers who accompanied the show's stars rarely survived the experience. Shortly after being beamed down, they would be vaporized, stomped or eaten for dramatic effect. It's a plot device so common that these expendable crewmen became known collectively as redshirts.
In his novel Redshirts, science fiction writer John Scalzi follows Andrew Dahl, a similarly expendable ensign as he sorts out this life-expectancy issue.
Science fiction is often a genre in conversation with itself; from Terry Pratchett's Discworld novels to Galaxy Quest, from The Walking Dead to The Purple Rose of Cairo, it thrives on metatext and a love of details. It's a place inhabited by loyal, passionate fans who are nonetheless acutely aware of — and happy to question — the minutiae of what they love.
In fact, it's a show's biggest fans who are most likely to be watching a starship crew suit up for a mission and asking the screen, "All three top-ranking officers are going? Really?"