Bill Belichick's two coordinators , Romeo Crennel (left) and Charlie Weis, are leaving to become head coaches. Rick Stewart/Getty Images

There's been so much talk about what the New England Patriots will do without Charlie Weis and Romeo Crennel that I've decided to weigh in on the topic. They'll be fine. Trust me.

If Bill Belichick can find a way to lead his team to a third Super Bowl title with two-way players and unknown reserves assuming key roles, he'll somehow manage with a new offensive and defensive coordinator. What I find more interesting, however, is how Weis and Crennel will fare without Belichick.

When Weis starts working full-time as Notre Dame's head coach this week and Crennel moves into his job as the Cleveland Browns head coach, both will be trying to beat history. It isn't an easy transition for NFL assistants who take head coaching jobs after working for teams as successful as New England's. Most end up failing, particularly if they aren't part of the Bill Walsh coaching tree. In fact, of the seven head coaches who have won at least two Super Bowls over the last 20 years, only two -- Walsh and his successor in San Francisco, George Seifert - have had a slew of assistants become impressive head coaches after serving directly under them.

As for the others, here's a list of their assistants who became head coaches:

1. Jimmy Johnson, Dallas Cowboys: Dave Wannstedt, Butch Davis, Norv Turner and Dave Campo.

2. Joe Gibbs, Washington Redskins: Richie Petitbon, Joe Bugel.

3. Bill Parcells, New York Giants/New England Patriots/New York Jets/Dallas Cowboys: Belichick, Tom Coughlin, Al Groh and Chris Palmer.

4. Mike Shanahan, Denver Broncos: Greg Robinson

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As I studied this list, I kept wondering why so many assistants from successful organizations disappointed as bosses. So I decided to call Walsh. I figured I couldn't lose. He's recently been teaching NFL seminars on making the transition from being an assistant to being a head coach. Plus, he loves talking about subjects that make him look smarter than his former peers.

This is what I took away from our conversation: It's a lot harder to become a head coach these days than it was in the past. They face more pressure from the media. They have to deal with more owners getting involved in the team's operations. They have to learn about the salary cap, sometimes on the fly, and they have to cope with inferior personnel. Even Walsh is willing to admit that his success, as well as that of his assistants, had much to do with the presence of a talented quarterback.

I also learned something else: Walsh had a system in place that served his assistants well. He identified coaches who he said had "executive potential" -- men like Shanahan, Seifert and Mike Holmgren -- and exposed them to all facets of the day-to-day business of the organization. "I directly involved them in nearly everything," Walsh says. "If we were making a team decision, they contributed to the process. And when they became head coaches, they were ready to deal with those situations."