Sure, we all love Ripley. She's a bad-ass alien killing machine and the standard bearer for generations of female protagonists to follow. But of course she’s not the only survivor of the Nostromo. She shares her survival with the unsung hero of the first chapter of the Alien franchise, Jonesy the cat.
Jonesy has an actual job on board the Nostromo -- he’s there to hunt vermin and pests that may have inadvertently ended up on the ship during its construction. As a bonus he's also there to provide some level of relaxation for the crew.
Considering that Alien is essentially a movie about a pest that stowed itself onboard the Nostromo, some of you might say that Jonesy failed at the one job he had. Fools, I say. You're all fools.
Cats do hunt pests, sure, but the true mark of a successful cat is not in his or her hunting ability. The goal of a cat, aside from getting scritches, which I will gladly provide at any opportunity, is to get humans to do tasks for them. Why hunt for mice, for example, when you can just mew at a cabinet door and let a person pour delicious nummies into a bowl? And like, litter boxes are a thing.
Given this reality, I think it's clear that Jonesy is actually super successful at his specific job.
Does he not get Ripley to go ahead and take care of that xenomorph problem for him? (Spoiler alert, he does.)
Earlier in the movie, when Ash's tracking system picks him up instead of the alien, you could argue that it’s just a coincidence that the xenomorph just happens to be in the same room where Brett finds Jonesy. I posit instead that this is Jonesy going, "Hey I found that thing you were looking for, if you want, you should take care of it." It's not his fault that Brett doesn't pay attention. That's why Jonesy simply watches, glossy-eyed, as Brett goes ahead and gets himself deaded.
Clearly what is happening here is that Jonesy is an expert at taking down xenomorphs; that's why when the alien does come face to face with our fluffy handsome boy, even trapped in his cool space-themed cat carrier, it leaves him be. It knows that trapped Jonesy is still Jonesy and you don't tempt fate by messing with Jonesy.
If you're not here to scritch, you just move along.