There are people who were at OpenDNS in the early days who were incredible, and as we grew, became less and less incredible, largely because the things that made them incredible actually started to be really frustrating as the company grew and they didn't want to change those things. So they had to leave. Usually it was a series of conversations about how the person, their peers, and the company were all unhappy, and…
Commandos are people who love challenges and hate structure. They'll happily take on missions that other people think are crazy or impossible, because doing things other people think are crazy or impossible is what turns them on. They get you your critical early beachhead by swimming in at midnight with a knife in their teeth and slitting throats till morning.
Infantry are what most people are. Most people are not Rambo; crazy suicide missions don't turn them on. But at this point you have your foothold on the beach, so suicide missions are few; what you need now is lots of people to take that foothold and widen it into a big enough space to sustain yourself on indefinitely. This work is kind of a grind, so it doesn't appeal to the commandos, who start falling away looking for a new beach to storm. But it's critical for turning the company from a proof-of-concept into a real, going concern.
Eventually the fight for the beach ends, and the battle moves inland. But you still need to have some people there to maintain order, which is where the police come in. Police are even more risk-averse than infantry; they're caretakers who see their job less as expanding the market the commandos and infantry have won then as making sure it doesn't fall apart. Commandos and infantry fight to win; police fight to not lose.
All of these personality types are important at varying stages in a company's life, he writes, but the big challenge is making sure you have the right ones at the right stages, and that you manage the transitions between those stages well. A mostly-commandos startup that takes off but tries to still keep itself mostly commandos will choke on its own success. A larger company that still has growth opportunities but phases out its infantry in favor of police too early will miss those opportunities and get ground down by more aggressive competitors. A company that's grown as much as it can grow but resists bringing on police will run itself down launching futile new products that the market isn't asking for. Etc.