Every NFL season is a learning process. Preconceived notions of the summer often are turned on their head by Halloween (if not sooner), while players whose names might not have even appeared in their team's preseason previews wind up being a cause for hope by the end of the first month (take a bow, Brian Hoyer).
Of course, the first month doesn't tell us everything. Keep in mind that at this time last year, the Arizona Cardinals, who finished with a 5-11 record, were 4-0.
Still, much has been revealed. Here's what I think we've learned after the first month of the season:
» Can anyone stop this Denver dynamo? Despite playing at an age when most quarterbacks are in decline -- and despite enduring a neck ailment that sidelined him for all of 2011 -- 37-year-old Peyton Manning is playing the best football of his life, and that makes the Broncos the team to beat in the NFL.
Manning arguably has a better receiving corps than he did in his best years with the Indianapolis Colts (though he obviously lacks a versatile running back like Edgerrin James or Joseph Addai). His arm strength looks to be nearly back to where it was before 2011, and I think we're at the point where it's safe to say Manning sees the field and reads opposing defenses better than any quarterback -- ever. As if that weren't enough, he's also even more comfortable with his receivers, eradicating the mistakes and missed connections of last year. Sixteen touchdowns, zero interceptions.
» Same old Patriots. While Manning has been dazzling, Tom Brady getting this New England team to 4-0 is nearly as impressive. Brady is throwing to -- let's be kind -- a cast of mediocre receivers, most of whom he's more or less just met. The team's best running back, Shane Vereen, was lost after Week 1. And yet, Brady has coaxed the Patriots to a perfect start.
» A clean slate helps. Trying to muster a new personality with the leftovers of the Pat Shurmur era, the Cleveland Browns floundered to an 0-2 start. But after trading away recent No. 3 overall draft pick Trent Richardson -- a move seen as tantamount to surrender in some circles -- the Browns installed Hoyer in place of the injured Brandon Weeden, and they've won two straight. You'd still bet on Cleveland going with a quarterback in the first round of next year's draft, but Hoyer undeniably has provided a spark that was lacking. (Of course, Josh Gordon's return from a two-game suspension didn't hurt, either.)
» Coaching experience counts. Take a look at the coaches who have their teams at 4-0: Bill Belichick (19th year as an NFL head coach), Andy Reid (15th year), John Fox (12th year), Pete Carroll (eighth year) and Sean Payton (seventh year). People talk about how much faster the game is for players when they come to the pros; it's also an adjustment for head coaches, whether they're moving up from being assistants or coming from the college ranks.
Terrific head coaches are like franchise left tackles -- there's just a handful of truly exceptional ones. The skill level of the vast majority of NFL teams is so similar, meanwhile, that coaching -- not just in terms of X's and O's, but also in generally guiding a team and building an atmosphere of accountability -- can be a decisive factor.
Payton's return seems to have energized everyone on the New Orleans Saints. It's not as though interim coaches Joe Vitt and Aaron Kromer did a bad job last year; they were put in a very tough spot. This season, though, the team has a crispness and focus it lacked for much of 2012. (The reinforcements on defense have helped as well.)
» By the same token, revolutionizing the league doesn't come easy. As I pointed out earlier this year, the league average for number of snaps per game has stayed around 65 for quite some time. A quarter of the way through the 2013 season, Chip Kelly's fast-break Philadelphia Eagles are averaging ... 67 snaps per game (slightly less than they averaged last year, before Kelly's arrival).
Give Kelly time. He's still trying to assemble the right cast, and he has an interesting mind. But the revolution won't come as immediately as some people who watched the first half of the Eagles' Monday night opener suspected it might.
» In the NFL, the next step always is the hardest. The St. Louis Rams experienced a revival under Jeff Fisher last year, playing their divisional rivals particularly tough, securing a 4-1-1 mark in the NFC West (including a tie and a win against the eventual NFC champion San Francisco 49ers). Many thought they were ready for a step up this year. However, Sam Bradford seems stuck at an average level of quarterbacking and the offense has been slow getting untracked (falling way behind in two September games). The team misses the presence of Steven Jackson, whose sturdy professionalism was the focal point of the offense for most of the past eight seasons.
First-round draft pick Tavon Austin shows flashes at wideout, but St. Louis seems in danger of taking a step backward.
» Creating takeaways and limiting turnovers -- still the name of the game. The 4-0 Kansas City Chiefs are a league-best plus-9 for the season in turnover differential. The Seattle Seahawks, despite not yet getting their offense in sync, stand at plus-7 and also are undefeated. Even the lightly regarded Tennessee Titans have bounded to 3-1 on the back of a plus-9 differential. Then there's the flip side ...
Two of the NFL's flagship franchises, the Pittsburgh Steelers and New York Giants, are sitting at the bottom of an 0-4 well, and this largely is because they possess the worst turnover differentials in their respective conferences (minus-11 for Pittsburgh, minus-9 for New York). These teams have 10 Lombardi Trophies between them, including four in the past eight seasons, but nothing's gone right for either franchise in 2013.
With Pittsburgh, you start with that offensive line. Of all the losses sustained by teams this season, the injury to Maurkice Pouncey might have been the costliest. The Steelers have lacked the drive up front to spring their running game (of course, before rookie Le'Veon Bell returned from injury last week, they didn't really have any difference makers at running back). More importantly, they haven't afforded Ben Roethlisberger the protection he needs to find his crop of green receivers. Checkdown security blanket Heath Miller's injury also hurt, leaving Big Ben with a dearth of reliable targets in the season's first two weeks of action.
In the case of the Giants, where do you begin? Mistakes. They gave away the opener at Dallas, then floundered from there. It's not like old-school paragon Tom Coughlin doesn't preach limiting mistakes, but it hasn't helped. The Giants haven't protected the ball well, and their running game has been mostly abysmal.
Despite the anguish in Pittsburgh and New York, all hope isn't lost. Both teams possess the means to recover, in terms of personnel (Big Ben and Eli Manning didn't suddenly stop being good quarterbacks) and upcoming schedule (after opening against teams that have gone 11-4, the Giants' opponents over the next five weeks -- a stretch that includes two matchups with the 1-3 Eagles -- are a cumulative 6-10, while the Steelers play the underwhelming New York Jets and Oakland Raiders in two of their next three games). Furthermore, both teams are just two games out of first place in their respective divisions. Despite the dreadful start, each team still controls its own destiny.
And that, perhaps, is what's most worth keeping in mind. Though several teams already have been crowned or left for dead, this is a marathon, not a sprint -- and 23 of the league's 32 teams are somewhere between 1-3 and 3-1. Of all the things we know, the one we have to keep returning to is the simplest: There's a lot of football left.
Follow Brian Billick on Twitter @coachbillick.