I've enjoyed science fiction from a very early age. From the comic strip adventures of Dan Dare and hiding behind the sofa from Daleks to methodically working my way through the sci-fi section at my local library I couldn't get enough of speculative worlds & futures. As a pre-Space Age child (Sputnik 1 was launched nine months after my birth) I latched onto the genre as a collection of signposts towards the (Brave) New World that was awaiting my adulthood, a land of wonders & terrors very different from my mundane surroundings. Or something like that.
By being, by definition, sited outside familiar situations sci-fi tends to require a fair bit of exposition. This lends itself nicely to literature where pages can be spent explaining the sociological structures of the Zarg Empire or the economics of 24th century Wiltshire but as stories started to be translated to visual media all this explanation could often derail the dynamic flow of the narrative. Having a minor character explain the significant characteristics of the Phase Disruption Cannon would defuse the excitement of a giant space battle but placing it earlier in the story would undermine the potential tension as the watcher is then just waiting for it to be used. Not explaining it at all is just as bad as the sudden reveal of the Super Weapon then becomes a Deus Ex Machina 'get out of jail free' card, removing any peril from the situation.
Some writers & directors have found inventive & creative ways around this problem, often by subtly foreshadowing the significant plot device, gently dripping in detail to slowly build up awareness, or by providing a metaphor that allows the situation to be viewed into a more familiar context. However this is sadly the exception rather than the rule and it's become the common solution to just hide the plot convenience behind a big explosion or some other distracting eye candy The adrenaline rush short circuits our analytical processes and it's not until afterwards that we realise that it made no sense.
Sometimes things are explained after the event, in the style of an Agatha Christie detective's final monologue where the seemingly unconnected clues are masterfully reassembled into a consistent & incontestable description of the crime. However this does tend to make the character insufferably smug and hard to empathise with, the implied "I'm so clever and you're not" quickly becomes irritating. I know Sherlock Holmes never actually said "Elementary my dear Watson" but it's easy to imagine the good doctor just decking him at that point.
An aside - I read a short story where a Poirot-like detective assembled all the potential guilty parties and painstakingly explained how each of them could have been the killer, at which point they ganged up, shot him, disposed of the body and agreed on a collective mutual alibi. Very satisfying.
Another way to approach this problem is to establish that the protagonist is skilful in that area and can be trusted to make the right decisions, so we can have Wash, Han or Starbuck drive their spaceship out of a tricky situation without having to explain orbital dynamics or thrust/mass ratios. Or have Scotty eject the warp core to blast the Enterprise free of a black hole's gravity - it makes no sense but we accept that he knows what he's doing.
However this brings up another point - the hero(ine) makes the right decision but it's the godlike power of the writer that makes that decision the right one. Where we have some real world experience we can see if the outcome seems plausible but when it involves setting the overload limiter on the flux drive we have no idea - is this a calculated adjustment, a risky ploy or a reckless, last-chance grasping at straws? The outcome will validate the choice but in a fictional world there's no external risk of failure, everything lies in the lap of the screenwriter. This is true of all fiction of course and we're always willing to allow a little bending of the probabilities for a good story but at some level things have to be at least vaguely plausible to allow any empathy - we'll often accept villains who can't shoot straight or ludicrous driving exploits but push it too far and it doesn't engage any more. Imagine a story where someone goes into a casino and wins at roulette six times in a row with no explanation - it would hardly grab the attention. (Actually this could be fascinating if it dwelt on questions of improbability, expectations and how we define reality but I can't see something like this getting commissioned).
Two more factors come in to play at this point. For a TV series or a film that hopes to become a franchise there will have been some investment in the primary actor(s) and extreme reluctance to kill them off. Added to this there's more and more action involved, the days of the quiet, cerebral hero are long gone. So we have the common situation of a protagonist who faces increasing levels of peril but virtually no real risk of suffering significant injury.
When talking to and reading about authors a common theme is that they create rounded characters, put them into interesting situations and 'observe' how they react rather than just lay out the plot line and fill in the gaps. This grounds the responses & reactions in their personalities and ultimately makes the whole thing more realistic and believable. By giving each character their own set of motivations, attitudes & idiosyncrasies and letting them find their own way you end up with a complex series of interactions rather than just several copies of the author's viewpoint. I've often heard writers talk about characters doing unexpected things and taking the story away from its original premise, leading in new and unplanned directions.
So, imagine yourself as an action hero in a sci-fi series. Slowly it dawns on you that you're never in any real danger and that basically anything you decide to do will turn out to be the right choice. Any minor injury you suffer can always be overcome with just a grimace or, if you want to make a meal of it, an angry scream. Is it any wonder that your sense of fear slowly turns to impatient irritation with the tedious plot details you have to work through to get to your inevitable triumph? That you begin to view other characters with derision & scorn, haranguing them when they're slow to appreciate your obviously better judgement and dismissing the futile machinations of your enemies with oh so carefully crafted one liners? As the story progresses the capricious god of your world continues to confirm your divine status and the lesser mortals around you become less and less significant to your holy quest. Which is a pretty good definition of a psychopath.
To be fair most writers will try to rein in their obnoxious creations before things get that far. A common device is to give them a moral dilemma by having to choose between two other characters, usually in a life or death situation. Their own safety remains assured, the risk is to their public image and the need to remain the Good Guy which is often their only remaining vulnerability. Of course they will always be shown to have made the best decision in the long run. Although the runaway hero can often be tempered in various ways there often remain traces in the dialogue - when a character exclaims that someone has to do something or must take a certain action there's usually a subtext of 'there's no justification for this, just accept that I am always right'.
The only time I've seen this progression explicitly explored was in the Breaking Bad TV series where Walt, the main protagonist, is slowly transformed from an understandable, sympathetic character to an amoral monster. The nearest thing in sci-fi is probably Laura Roslin in the 2004 version of Battlestar Galactica, a low ranking official who is thrust into power and then will do anything to remain in control (note, this is not an uncontested assessment).
In most cases we're left with an obnoxious, sarcastic bully who the other characters defer to, logically observing that they really are touched & protected by a divine power. And in some ways that is a tragedy in itself, an individual corrupted by an absolute power that they never sought in the first place. Although I appreciate that killing off a major character isn't really practical in the production of ongoing TV and film drama nowadays (if indeed it ever was) it's a shame that the increase of action scenes to boost perceived excitement actually devalues itself by resulting in meaningless non-peril. In the end it's all down to poor (or at least formulaic) writing and the substitution of spectacle for ideas, which I suspect is nothing new but is a drag for those of us with trashy tastes. Sigh!