New England quarterback Tom Brady — who did not play in the preseason — will have his sights set on Kansas City’s defensive secondary this afternoon at Gillette Stadium in Foxboro.

>

The Providence Journal / Glenn Osmundson

You’re standing at the edge of a Mexican cliff, staring at the crystal blue Pacific about 125 feet below, getting ready to jump for the first time. It could be an exhilarating experience or it could be something that’s pushed from your mind as quickly as possible.

Bill Belichick and the New England Patriots are standing on that ledge, ready to jump into their season against the Kansas City Chiefs.

Their opponent, the end result of the game, what will happen over the next 16-plus weeks — are great unknowns.

It could be exhilarating, or it could be something that’s better forgotten.

The Chiefs themselves and the 2008 season pose similar parallels: New England hasn’t faced Kansas City since 2005, before Herm Edwards was coaching there, before Chan Gailey became offensive coordinator, and before roughly 85 percent of the Chiefs’ roster joined the team.

But not only is much of the personnel unknown, what those players might do on the field is a mystery as well. Most clubs go vanilla in the preseason, holding back new plays or formations until the games count.

“This is a case where a majority of players on that team, we haven’t played against. The last time we played them it was a different system. There’s a lot of newness there,” Belichick said earlier last week. “There are a lot of unknowns.”

New England will be trying to feel out young players as well as get a feel for the Chiefs’ play-calling tendencies, though those might be easier to figure out. Defensive coordinator Gunther Cunningham has kept things fairly similar over his 11 years on the job, and Gailey hasn’t changed his system much, whether he was with the Dolphins, Georgia Tech, or now in Kansas City.

There is a higher-than-usual level of unpredictability to today’s game.

It is nearly as unpredictable as what could happen this season, which is where much of the excitement of the start of the season is derived.

One of the most frequently heard refrains when current and former Patriots players are asked about Belichick is that he always has his team prepared for nearly every possibility that could come up during a game.

But Belichick can’t prepare for the unknown. He can come up with a loose sketch for the season, how he’d like to see things go or what might happen if pieces A, B, and C fall into place.

Some things, however, can’t be predicted. No matter how he tries, there are things Belichick won’t see coming.

Take Sept. 23, 2001, a day that forever changed the fortunes of the Patriots. At the beginning of that day, Drew Bledsoe was entrenched as New England’s starting quarterback, was paid handsomely, like the face of the franchise that he was.

One hit from the Jets’ Mo Lewis later, a skinny, green second-year kid named Tom Brady takes over.

Handing Brady the Pats’ offense was a little like standing on that rock ledge, and that turned out to be exhilarating — three times over.

There are so many events, events which at the time seem innocuous or can immediately be seen as season-changing, that can occur over the course of a season. An injury that ends up devastating the defense or which opens the door for a future star to grab his chance; signing a largely unknown free agent who at first seems like a depth pickup and blossoms into a Pro Bowler; calling for a ‘go’ route when a seam route might not have resulted in an interception.

That’s part of the reason Belichick admits to having butterflies in the moments before every season opener.

He and his staff and players have spent the last six months improving themselves, improving their team, preparing for the long season ahead of them.

This morning, they climb to the top of the cliff, the season before them like the blue Pacific, ready to jump in.

smanza@projo.com