Back when I was in business school at the MIT Sloan School of Management, one of my favorite professors was Howard Anderson. Howard, a very successful serial entrepreneur, founded both Battery Ventures and The Yankee Group, and in his "retirement" teaches a full course load to MBA students at Sloan. Howard's classes are a must-take for any MBA who aspires to start a business or run a business.

One of Howard's favorite things to do is ask students if they are an attacker or a defender, because if you know what kind of person you are, then that will determine the type of company you join when graduating.

The way that Howard defined attackers and defenders is simple. If you are a company at the top of your industry, then you are a defender. You have everything to lose, and very little left to gain. Sure, you need to grow your revenues and you need to remain profitable, but really, the only place for you to go is down. The prototypical defender is a company like IBM. Many people in the tech industry joke that you can never get fired for buying from IBM, nor can you get fired working at IBM. While that's probably untrue, there is probably also a little bit of truth said in jest. IBM is a profit-machine; it just keeps rolling along, and is proof of the old adage, "You need money to make money."

Conversely, if you are working at an attacker, then you have nothing to lose and everything to gain. The obvious example of an attacker is a start-up, where you have an idea, some talented people, and very limited resources that force you to be scrappy and think creatively. But don't assume that every attacker has to be a start-up. I'd submit a company like Novell, where I work, is an attacker. Novell at one point was a defender with its NetWare franchise, and there was this little company called Microsoft that was the attacker with its Windows NT platform. Fast-forward a decade or so, and now Microsoft is the defender and Novell is the attacker, as we try to fashion a turn-around here at Novell and return the company to glory.

It's this very reason that I turned Microsoft down when I graduated business school in 2004 to join Novell. I wanted to join an attacker. It seemed more interesting to go after the opportunity and ride the growth than it seemed to go work at a company already established on top. Besides, at Microsoft, I would have been one of 500 MBAs hired that year, and at Novell, I was the MBA hired that year. Granted, Novell had more risk in it, but with that risk came opportunity.

Being an attacker should be a liberating feeling. If you work at an attacker, that attitude should permeate everything you do. An attacker should be thinking about how do I get that edge, what chance can I take, what angel can I play that will accelerate my path to the top? An attacker can afford to take risks because they have to do so. Conversely, defenders have no incentive to take risks because if you take a risk and get it wrong, then you risk coming down from your pedestal.

I try to be an attacker in all aspects of my professional life, because I find it to be more fun. It influences the positioning work that I do … making a claim and forcing my competition to knock me from that perch. It influences my hiring philosophy, because I want my team to be driven people who will take a chance to win. It influences my attitude towards meetings, where I have a bias toward action as opposed to delaying decisions to the next meeting.

As you think about your own career, and as you ponder your next career move – whether it's today or next year or in five years – I'd submit it's important to know what kind of person you are, and what kind of role you want. An attacker in a defender company will quickly become frustrated with the slow pace of things. Similarly, a defender in an attacker company will be forced to make decisions outside his or her comfort zone at a speed he or she doesn't like.

The bottom-line is that the world needs both attackers and defenders. Neither one is better than the other… it all depends on the type of person you are. After all, neither one could exist without the other.