First Round Capital writes about Keith Rabois' talk about the role of COO:

During Keith Rabois’ first week at Square, Jack Dorsey asked him to deliver a speech to the company about what exactly he would be doing as the chief operating officer.  Square was just 20 employees at the time, so it wasn’t clear what a COO would or could do for such a small company.

While crafting what he would say to the team, Rabois developed a simple metaphor for the role of a COO at an early-stage company: an emergency room doctor.  Just like in the ER, there’s always something broken at a start-up, it’s incessantly chaotic. There can be issues that seem to be just a cold, but they can actually be fatal if you don’t address and fix them early on. Also, there can be other kinds of issues that seem to be serious, but in actuality they’re just everyday colds and they’ll clear up on their own.

The same types of situations exist on the pure business side at any startup. There are opportunities that may look really interesting and potentially compelling for the business, but they’re really just a distraction.  Conversely, there are things that look like a distraction, but they could actually turn out to be really important and just might be gems.  The hard part of scaling is how to figure out those things and to find the truth in all of it — that’s the job of the COO.  You’re constantly fixing things.  You assess a problem or opportunity, fix it, put concrete down, leave it stable, then go on to the next thing.  Then, over time, if you lay a foundation and everything’s fixed, you can build on top of it.

That's fine but I think I differ in the definition of "early-stage".

A 20-person startup is not early stage.

On startups and hiring:

Getting leverage as an entrepreneur is all about hiring the right people. That sounds easy, but it’s actually really, really hard.

At the very first board meeting Vinod Khosla attended he said, “Ultimately, the team you build is the company you build.”

It is the team you build that will dictate the outcome. This belief should lead you to focus more on the quality of the people than anything else.

If you think about people, there are two categories of high-quality people: there is the ammunition, and then there are the barrels. You can add all the ammunition you want, but if you have only five barrels in your company, you can literally do only five things simultaneously. If you add one more barrel, you can now do six things simultaneously. If you add another one, you can do seven, and so on. Finding those barrels that you can shoot through — someone who can take an idea from conception to live and it’s almost perfect — are incredibly difficult to find. This kind of person can pull people with them. They can charge up the hill. They can motivate their team, and they can edit themselves autonomously. Whenever you find a barrel, you should hire them instantly, regardless of whether you have money for them or whether you have a role for them. Just close them.

In addition to trying to hire all the barrels you can, at a start-up every marginal person you hire should be relentlessly resourceful. There are people who are just better than others at getting things done, and those are the kind of people you need in large numbers early on.

If you can build a team that’s barrel-heavy and is relentlessly resourceful, your job as the leader of a company is really to just be the editor — a concept that Jack Dorsey has now made mainstream. Every time you do something, you should think, “Am I writing or am I editing?” You should be able to tell the difference immediately. It’s okay to write once in a while, but if you’re writing on a consistent basis in marketing, or in legal, or in product, or business development, or whatever the case is, there’s a fundamental problem with that team. Get into a position where you are editing all the time.

The analogy of an editor is great, because what an editor does is not the work product. Think about a reporter. The reporter writes the story. The editor may ask clarifying questions. The editor may simplify and extract things, edit things out or leave things in, or occasionally reorganize things that require follow-up. But, fundamentally, editing is the role.

He also has this money line: At a startup you can often be tricked into thinking you’re building a technology company and so you focus a lot on the product, but ultimately what you’re really building is a team to build the product and then the company.

Hiring is the most important thing a startup can do.

Other than, you know, surviving.