Okay but imagine you're Eva Stratt
You've been waiting for literal decades to hear if that spaceship you sent out with three comatose astronauts (one of whom you kidnapped and drugged and wiped his memory to force him to go along) have figured out anything that could possibly help save the earth. The probes finally splash down and are successfully retrieved. Inside are canisters labeled "Taumoeba Farm"
The fuck is a "taumoeba"? you think, and very carefully hand it off to some scientists, because you're not some idiot that would unscrew a strange capsule from outer space in a nonsecure environment. That shit could be full of ammonia or toxic gases!
So, you boot up the video diary, hoping it will explain what to do, and, hey! It's your favorite little science guy (whom you kidapped and drugged and forced onto a suicide mission). He survived! At least for a while, since he's certainly dead now. The other two crew members did not survive. Oh dear. So it's up to this amnesiac scientist who can't fly a spaceship to save the planet. At least he hasn't remembered that he doesn't want to be there yet. Perhaps you should warn those scientists not to open the "taumoeba farm" in case this is the scientist's idea of revenge. But so far he seems to be doing well, figuring out the mission, locating the Petrova line...
And at this point you're really regretting giving him all those drugs, because they've clearly had some adverse affects. He's hallucinating. The Earth is doomed.
Your favorite science guy keeps going on about his new little alien buddy and puppet shows and clearly this is an elaborate delusion his brain has cooked up to keep him from facing the reality of slow, lonely death in space and—
Your favorite little science guy whom you led like a lamb to the slaughter is whispering and the alien has apparently invaded his spaceship and he doesn't seem nearly as alarmed by this as he should be if it were real. And then you hear a robotic voice answering him from offscreen and you think oh, Grace, you really programmed the ship's technology to feed into this delusion? You can't believe you're going to be court-marshaled and jailed because you did so many crimes just to get this scientist into space just for him to blow it all because he's so lonely that he made up an imaginary friend!
And then the camera pans and in the background you see—
There is sentient life elsewhere in the galaxy. Humanity is not alone. Ryland Grace is apparently perfectly sane...
You barely have time to process this before the video ends and the next video diary starts up.
The alien is making the video diary.