You can manage 50 people through the strength of your personality and lack of sleep. You can touch them all in a week and make sure they’re all pointed in the right direction. By 150, it’s clear that that’s not going to scale, and you’ve got to find some way to keep everybody going in productive directions when you’re not in the room.
I met Mark once, and from what I could tell he operates at a frenetic pace all of the time. So perhaps at that frenetic pace he can touch 50 people in a week, however the number for most mortals is much lower. I max out around 20. So if you plan to scale, you have to delegate effectively, and that's one of the biggest challenges people face when they turn into 2nd level managers. You need to delegate completely so that you don't have to worry about the details of a particular function, but you also are still responsible for it being done properly. So how do you know if the person you've delegated to is up to the task?
You have to first make it clear to everyone what they are responsible for and give them all the tools they need (Gallup Q12 #1 and #2). One of the most important tools is the ability to make their own decisions in that framework (Zod axiom #4). Once you've made the responsibilities clear, you then have to hold people accountable. You have to set up the right mechanism to check in on people and make sure they're getting the work done properly so you can catch mistakes before they veer too far off course. Setting milestones and regular reviews of them are key. You trust your people to perform well, but you check on them anyhow.
One thing I did at my second company was to put white sticky sheets on the wall, and I put everyone’s name on one of the sheets, and I said, “By the end of the week, everybody needs to write what you’re C.E.O. of, and it needs to be something really meaningful.” And that way, everyone knows who’s C.E.O. of what and they know whom to ask instead of me. And it was really effective. People liked it. And there was nowhere to hide.Here I like the concept, but not the implementation. By calling people C.E.O.'s he's making it clear that all of the responsibility and accountability goes to the person. If you're CEO of selecting a phone system, then you are tasked with gathering the input from everyone, evaluating all the vendors and making the decision. Important here is that you own the decision, there isn't a committee of deciders among which to share the responsibility. The credit/blame resides fully with one person, and that provides accountability.
His implementation leaves something to be desired, however. He's asking his team to sign up for responsibility and then he'll hold them accountable for it. That will work provided that no two people sign up for the same responsibility, and that all of the responsibility you want to delegate gets assigned. If two people both agree to be CEO of phone vendor selection, then now you've got a committee and shared decision making, which just doesn't work. Further, if nobody signs up to select the phone vendor, then either you're left with that responsibility, or (more likely) the work won't get done. So as a manager, you want to solicit input from your team on what they want to own, but ultimately you own the responsibility for dividing up your responsibility in a way to ensure everything is covered and nothing is left undone.