NFL strategy is cyclical. No one understands this elemental truth better than Patriots coach Bill Belichick, who has proven once again to be at the vanguard of an inverse reaction to conventional wisdom.
While the rest of the league was copying his two-tight end offense, Belichick was steering his team toward a stout ground attack that has finished in the top 10 in back-to-back seasons.
Once defenses countered the trend toward pass-heavy offenses, the obvious answer on offense was a move toward power football, taking advantage of mismatches against softer nickel and dime defenses.
That dynamic was on display during Divisional Round Weekend, as no winning quarterback topped 230 passing yards.
Pete Carroll and Jim Harbaugh have built the Seahawks and 49ers on physical, ball-control offenses and smashmouth defenses. Peyton Manning and Tom Brady are two of the rare quarterbacks savvy enough to check to the run at the line of the scrimmage when the advantage is there to exploit.
The NFL might be a passing league in the Indian Summer regular seasons, but it's a different game outdoors in January.
It's only fitting that the four teams with a shot at the first cold-weather Super Bowl churned out an average of 167 rushing yards in their divisional round conquests.
Here's what else we learned in Sunday's games:
1. From the "it's never too old to teach an old dog new tricks" department: John Fox placed the ball in Manning's hands late in the key moments rather than nodding to a faint notion of "playing by the book" and running his tailback into the pile as a fruitless clock-burning exercise. True football epiphany or not, it's a promising sign for the Broncos going forward.
2. Another promising sign: Denver's beleaguered defense has held four of its past five opponents below 260 total yards of offense. That will be put to a severe test against the Patriots' steam-rolling ground attack.
4. Harbaugh is the first coach since the 1970 merger to lead his team to the conference championship in his first three seasons. He and his coaching staff are arguably the NFL's most brilliant at game-planning and adjusting.
5. Harbaugh's Sunday fate turned on another standout postseason performance from Anquan Boldin, who pulled down receptions of 12, 14, 15, 16 and 45 yards as the 49ers pulled away on a pair of scoring drives leading into and coming out of halftime. If Richard Sherman shadows Michael Crabtree next week, it will be a challenge to shut down Boldin and Vernon Davis.
6. Having won eight straight -- including road victories in Green Bay and Carolina -- the 49ers are the hottest and most complete team left in the postseason pool. This will be a stiff test for Seattle's extraordinary home-field advantage and historically great pass defense, as San Francisco is a much tougher out now than they were in their last trip to CenturyLink Field.
9. It's back to the drawing board for the Panthers and Chargers. With Steve Smith entering his mid-30s, Carolina desperately needs a downfield playmaker at wide receiver. They were one of just three teams that managed to top 275 passing yards in a game only once all season. As we saw again on Sunday, the secondary is exposed when the front seven is unable to muster a consistent pass rush. There's a need for a big, physical cornerback as well as a safety.
10. The Chargers had the fewest three-and-outs in the NFL this season. Now that Keenan Allen is emerging as a viable No. 1 receiver and Ladarius Green's role is expanding, the only major need on offense is up front. The defense desperately needs playmakers -- specifically pass rushers and cornerbacks.