I think a lot people go indie with this mentality:
"I'll try making a game and see how it does. If it tanks, I'll go back to my day job."
With the result that they spend their last dime or even leverage themselves into putting everything into that first game, and then hope its sales will cover the next one.
This approach has worked for several well-known indies, but there's survivor bias going on there. If you start looking at failures, you'll see a ton of "we made one game and gave up" stories. There are also a lot of indies who bet everything on the first game, then have to scrounge around for funding for the next one.
Because most - dare I say, "almost all"? - games fail to make a profit.
Before Kickstarter, the way we had to scrounge was to do work-for-hire or give everything to a publisher. (And we had to compete at terrible terms for those deals!) And once we do that we're not indie anymore. That was the story of my previous indie studio, Torpex Games, which, after making Schizoid, then made Bejewelled Blitz LIVE to pay the bills (it was still a great game, though, IMO), and finally crashed and burned chasing publisher funding for an in-house title. Even if we'd gotten that funding the terms were terrible - we were giving away the IP and there are almost never royalties in this industry. We wouldn't have been indie anymore.
Now that there's Kickstarter, it is possible to throw out a lifeline after your first game tanks. Matt Gilgenbach is doing this right now. He has grit. He's still trying to make a go of the indie thing, even after Retro/Grade was an admitted flop. I really hope it works for him. He's asking for a lot but it could happen. I backed!
Besides having your first game be a hit, there is another path to indie success, which is what I'm trying right now, and has worked for others - a slow growth model where you spend as little as possible as you gradually grow your community. Introversion could be the poster-child for this. After Uplink they had to go on the dole while working on Darwinia - and though there was some luck in their history (Darwinia getting picked for Steam, by example) - some of that luck they generated themselves, by simply never giving up. Grit. Only now, with Prison Architect, do they finally seem to have found financial security.
Another reason to not give up after one game: you won't be able to benefit from the hard lessons you've learned.
No cut-and-dry rule of thumb here, though. There's definitely something to be said for banking it all on the first game - after all, a game's success is nonlinear, and if that little extra effort is what pushes your game to the front of the pack, it could mean the difference between hit and miss.
And there's probably also something to be said for knowing when to quit.
But giving up after one game is too soon.
On that note, check out Energy Hook. It's Happion Labs' second (but hopefully not last) game.