If you pay attention to some of the details that normally don’t matter much in a sci-fi story, and that are just ancillary aspects – narrative sugar, if you like the definition – you’ll notice several fallacies and mistakes that are so common that they have become invisible to your eyes. This is particularly true in sci-fi from the Seventies and Eighties.

And I’m not talking about flying cars here.

The first and most obvious absurdities are computers. 99% of stories get them wrong on two different ends of the spectrum.
One is the bulky, enormous computer with hundreds of blinking lights, green-phosphor screens, and monster keyboards with above a million keys. Ah, the Seventies.
On the other side, there are computers so advanced that can understand human language and act upon it, no matter the inflections of the characters’ voice, the accent, and the dialect. I believe this version is from a time when progress in electronics and software went so fast that something like that sounded possible, if not probable. We’re almost there with voice recognition, but that’s the easy part. Machines are still like cavemen in terms of understanding the infinite semantics of human language. Perhaps one day…

The second evident mistake, especially in movies, is the pervasive, panacea-style use of servo-motors.
You see automatic doors everywhere, for starters. You see motorized drawers or wardrobe doors. The funny thing is that a simple action like opening a door takes much more time when you have to wait for it to open by itself!

The last fallacy is humanoid robots (which are computers with servo-motors, sprinkled with sensors).
The point with robots is that they can do a certain limited, well-defined task  faster or more accurately than a human. A welder robot is just an arm with as many degrees of freedom (joints) as possible, with as precise mechanics as possible. A soldier robot might have threads to move on uneven terrain, or even better it might fly to get a vantage point on its target (BTW, military flying drones have been in use for quite some time).
The shape of the human body is as it is because, over hundreds thousands of years, it evolved to survive in an environment that requires a very high level of flexibility – for example, walking and holding something at the same time (an object, a weapon, etc.), thus legs and arms. We have frontal eyes because we tend to be more hunters than preys. Human hands are a wonderful piece of mechanics: they are very precise and versatile, but not really strong, and not exactly resistant to injuries.
Building a human-like robot certainly helps in integrating it with real people, but at the same time it hinders its versatility and therefore its usefulness. In a way, a robot trapped inside a human body sounds like a sad concept.

And the list could go on… what other wrong patterns did you notice in sci-fi stories and movies?