Chekhov's Pulse Laser Pistol
If the pistol isn't a red herring, ignoring it after its introduction in a science fiction novel not only leaves a plot hole but also a gap in the fabric of its world. Of course, unless it's done with subtlety, wit and concision, worldbuilding can quickly become as tedious as a list of plumbing parts. Which is why, perhaps, so many science fiction novels fall back on a generic future with a common, consensual backdrop. Worlds of secondhand furniture, drawn from easily recognisable histories. Ikea worlds whose products only sometimes require assembly, using easy-to-follow instructions and simple tools, and furnish scenarios as clean, utilitarian, and anonymous as catalogue illustrations. Where Chekhov's Pulse Laser Pistol is probably called Bob. Good old Bob. He's so familiar he's practically invisible. No need to describe him, or worry about the implications of how he got there, or the consequences of using him, in the last act. Along with everything else in the catalogue, he's a prop in a fantasy future shorn of actual context, much like pornography.