If the story can work above and beyond what the audience knows is reality, it's easier.
If the story can work above and beyond real life physics, it's easier.
In the end, making the unreal feel real has to count somewhere in the chain. Ultimately, it's down to a combination of script concepts, dialogue, and acting to sell the impossible, and within the genre(s). Sci-fi and fantasy are lumped into one, despite having disparate rules and how most sci-fi shows still do use fantasy.
Space 1999 - the premise was bunk, even then. It was sold on the drama and philosophy. Even then, the show - amazingly - has the verve to bring up scientific principles in the show that are actually true. In a show that's based on an iffy premise. Their proverbial slight of hand did wonders, if people were willing to look beyond the theme music. But a fun tangent, this show - for once - has more lasting benefit by having its real location be Earth. As, given what we know of the moon and its properties (see list below), it's easier to generate more plotlines than what S1999 did with the moonbase occupants trapped but lucky enough to have such busy lives -- and S1999 does impress me in a number of episodes... I'm amazed no sci-fi in the 70s focused on Earth if, theoretically, the moon went bye-bye. They covered almost everything else...
- Moon controls tidal waves and thus part of the ecological process as we currently know it - I believe this is a more distant discovery but not nearly as recent as moonquakes?
- The moon already is drifting away from Earth, at about 1" per year
- If there's any cheese involved, it was left behind by one of the astronauts
- The moon is contracting and even has earthquakes due to all the stuff we put on it (think relative scale) - okay, this revelation is a new discovery, reported over the last year or so
- Frank Zappa's daughter shares the moniker and her song "Valley Girl" was intended as a satirical statement on the Valley subculture of the early-1980s
- Craters are cool
- etc
I could buy into the Force, even if the 1977 original feels like it was about to say "There is no Force, you just had all that practice shooting wamprats from a considerable distance and this is the same thing but on a bigger scale", though that was also limited in scale and scope. Once it was made to do anything on a whim, it got too much as it also begs obvious questions on how nobody else, even the biggest Jedi of them all, had no inkling? (Or Yoda kept it all a secret, okey dokey then.)
I could buy into the light sabers due to limited function and presentation. For all we know, they're retractable, electrified swords and not the way that fans thought of later on over time. And maybe one day light can be harnessed in the way a sword is utilized. Still, bringing a sword to a gunfight is no less dumb.
Like the sonic screwdriver from Doctor Who, a device with a stated purpose (and allowing for some wiggle room within reason that fits the original scope - a unidirectional beam of ultrasonic noise to controllably push objects or start a fire being coherent examples. Once it was used to reprogram a computer by the flick of a wrist or acted like a tricorder or shield generator - it's no wonder a Tereleptil zapped it until it went boom boom... It was more fun back in the days when the Doctor had pockets full of goodies, which felt more grounded, and not a "Swiss Army Screwdriver". To the point I reveled with glee when the "Fugitive" Doctor asked what it was and wondered why anyone needed it before mocking it. Then again, an alien character that once regenerated due to a great fall now can fall from a much further-up distance and be fairly unscathed. Regeneration is fantasy based on science as extrapolation, noting how some simpler creatures can regrow legs if cut off and other neat things the more complex ones largely can't do... but it was easy to buy into. At least before a regeneration put out enough fire and energy to destroy entire Dalek fleets or wreck spaceship interiors that then have said flambe-Doctor get flung out due to the ship now out of control... scale and scope, in relation, and presentation - and everyone's different in what they will suspend disbelief over. It's inevitable, but one more example is this:
Heck, the TARDIS - as told initially - a machine that could travel anywhere in time and space, whose camouflage unit finally broke down while on Earth (after a lot of recent travel and harrowing escapes by the Doctor and Susan) just felt real. Suspension of disbelief wasn't difficult for sure, based on how they told it. Which is amazing, given how no technobabble or winkytink jokes needed. (A couple of episodes did beg questions, but that's another story.) Best of all: The 4th Doctor's explanation to Leela (in "The Robots of Death") was all that was really needed, and said explanation was never bettered so far. The real fun was in Ian being mindblown over what he (the scientist trope) thought was impossible.
Oh very well, then - her's one last bit: So why do I think the psychic paper is a load of bunk? Since the day it was deemed hypnosis as a real concept was debunked, even if it's still fun to see Delgado and - to a lesser frequency, Ainley - use it... kudos to the actors... I shouldn't dislike it as much, since the Doctor and Master both executed hypnosis before and with technology to project... I could roll with it. But as a piece of paper? Even energy radiating from a monacle or projectile beam is far easier to swallow.