There's a fabulous essay going around the 'net entitled The 11 Laws of Showrunning, and while the content of it is almost entirely about being a showrunner— someone with a lot of responsibility for a lot of other people, including the staff writers, set designers, sound and lighting, and the dozens if not hundreds of other jobs associated with producing a whole season of a television show— much of what Javier Grillo-Marxuach wrote there can easily be applied to any project that extends over multiple episodes, even if there's only one person at the wheel.
The one that really struck me is the second law: "Know what your show is and tell everyone." Javier then goes into detail that it's not enough to get the pilot aired and then tell the writers, "Give me the rest of the season. I'll know it when I see it." He says this is a common problem, that the showrunner hasn't thought about what this creative effort is, what it's trying to say, what positions it argues, what tone it expresses, what emotions it's meant to arouse. Even if they know it, they haven't put it into words concrete enough for the rest of the team to express clearly.
I think it's important for writers who work alone to also know all the things that go into your story. What's the theme, what's the premise, and what the series is. The last is nebulous, but it could be about many different things.
It was probably a mistake to ask, "So what are The Journal Entries?" Well… they're about mostly ordinary people who live in a complicated casual space opera setting full of aliens, biomods, furries, taurs, robots, uploads, cyborgs and artificial intelligences, and how they find love and and sex and other sensual pleasures even when the universe is seriously weird. The principle themes of the Journal Entries is that for those people who stay people, finding love and affection are hard, hard choices in the face of temptation have to be made, and sensual pleasures are truly worth the price of admission. It argues that humanity is worthwhile (almost at a Patrick Stewart Speech level) because it's messy and fun and conflicted.
This may be why some stories failed. The Lost Crew of the Palantir wasn't about that. It tried too hard to be a coming of age story, an adventure novel, and a first contact novel, but it wasn't about the ever-going fight we have to make pleasure and connection a centerpiece of our lives.
What a series is is bigger than the theme and the premise. It's closer to the premise. Certainly, the Journal Entries is always about sex and love, and there's going to be a lot of sex in any Journal Entries story— if there isn't, I'm Doin' It Wrong. The emotion it's meant to arouse most strongly is an arousal associated with identity: I hope my readers see themselves in the characters about to get it on. But it's also meant to be cozy, friendly, and a bit confusing, like a good life. But theme is often isolated to a single story, and it's often different from episode to episode.
What a series is is the theme and premise slammed together, and each arc or episode has its own plot and story, sometimes even its own characters, and its own themes and premises. But just as a serious central plot may have comic subplots, and just as secondary characters may actually have their own stories that get told, a series may question its central theme-and-premise, but it must never ignore or betray it. That way lies failures.