Evan wrote in February 2012 on Branch:

If you like to start companies, have resources, and have many ideas, it's tempting to not want to limit yourself to a single opportunity. Call it "parallel entrepreneurship" or the "studio model," the idea seems increasingly popular.

I’ve always been attracted to this notion and have tried it more than once. Lately, I'm valuing focus more and more. Curious from those doing it what they see as key — and, from others, if they think it might be a trap that keeps people from doing bigger things.

The discussion continues with John Borthwick, Michael Jones, and Max Levchin.

But the person whose words resonate most with me are John Lilly's:

I think it's so hard to get just one thing that has real impact in the world that most awesome entrepreneurs will feel strong gravitational pull towards "the one that works". So it seems to me that it takes very unusual team to be (1) awesome, (2) low ego, (3) able to attract world class entrepreneurs and then let them go work on the interesting project.

Seems very possible, but only a few teams in the world likely to really make it work - unusual mix of characteristics.

Personally, I think it's hard enough to get just one thing right.

So my rule of thumb has become: When in doubt, drop it.