I think people get the wrong impression of Stella. Her abilities reward failure, but there are really two ways to go: failure with success, and failure with “not caring about success ”.
What makes her so special is that there are so, so many survivor cards that reward failure. Predestination, take heart, rabbit's foot, “look what I found“, Live and learn... So if you’re going for partial success, you have the option to fail in your first and second action and set up your third and fourth. What’s great is, even in campaigns like the dream eaters where there aren’t many skill test on your encounter cards, you can slot the new level zero “test of will” to either get rid of a treachery or gain an extra action (and probably a card, because rabbit's foot is the best fit for an accessory.)
Permanents like a quick learner, which would be poisonous for most other survivors, let you fail early and succeed later. In fact, a -1 to future difficulty test means that you’re going to face automatic successes, especially if you’re dodging a low agility enemy, hitting an acolyte or group of rats, or using your old key ring to investigate a three shroud location. (Vital to appreciating this card: knowing that it doesn’t apply to the mythos phase. Your stats are safe there.)
In solo games, you’ll be able to persevere/bungle your way through skill test and fights with “neither rain nor shine”, getting these amazing +3 bennies, recurring with resourceful, and later True Survivor. Or you can rely on the Mysterious Raven to attack your sanity in exchange for one action clues, and heal with Grimm's fairytales.
In a group, you’re likely to get in a flex role: you’re great at agility, and with dark horse or the right skill cards, can be good at a few other things. Sometimes, with Peter S by your side, it’s soaking fear or dodging enemies. But Stella has a surprising role that is harder for other survivors to play: support. Neither rain nor shine allows you to give +3 wild skill icons to fellow investigators. Plus, it gets rid of the sting of failure. Some scenarios have cruel effects that, when resolved, can defeat you, take rounds off the scenario, or drive you insane. Not anymore.
You’ll have a lot of options to pick through as you gain experience, because the chainsaw and your .18 derringer both reward a failure first style. True survivor and drawing thin, while expensive in terms of XP, make an amazing late campaign engine.
Playing Stella will have you saying weird things though. Things like “darn, I succeeded all of my actions!”, or bragging about how how only the grit of the Postal Service can take on the horrors of the universe. So watch out for that.