The crazy yo-yo of NFL quarterbacking.

When you write a sports book about a team’s previous season, as I did in 2009, telling the story of the 2008 Green Bay Packers, you have to make judgments about players that get set into the cement of printed pages and which later, depending on how the players do career-wise, can make you feel lucky, or dumb as hell.

I got lucky with quarterback Aaron Rodgers (perhaps you’ve heard of him), and wide receiver Jordy Nelson. Rodgers replaced living-legend Brett Favre in 2008, and though neither he nor the team had an especially great season (Rodgers threw 13 interceptions, a career high through 2017; the Pack went 6-10), the former Golden Bear displayed lightning footwork, moments of uncanny accuracy, a quick brain, and a cannon disguised as a human arm that saw him launching the rock on 60-yard arcs to receivers running go-routes.

Even in 2008, Rodgers had games that incinerated the reports of those NFL scouts who looked at his college work and concluded he “lacked arm strength” and “couldn’t throw the long ball” — these are actual quotes — and warned if you drafted him you’d be signing a dink-and-dunker with weird mechanics who’d never be more than a game “manager.”

But it turned out the guy taking over for a very disgruntled Favre — the guy whose story-in-the-making had me move from L.A. to Green Bay in summer 2008 — possessed signal-caller skills so elite that Aaron Charles Rodgers now comes up anytime football observers start discussing the greatest quarterbacks in the history of the game.

So I got lucky. We put Favre on the cover of the hardcover edition, because everyone on the fucking planet practically had heard his name by 2009, not least after the months-long retirement-unretirement-revenge-will-be-mine soap opera that ended up with the Ol’ Gunslinger playing for the New York Jets (wha??). But for the paperback edition? Buyers of the book were greeted with a photo of the Californian, future boyfriend of Olivia Munn, and I got to write a new afterword covering the Packers’ 2011 Super Bowl win.

Jordy Nelson caught nine passes for 140 yards in that 31-25 victory over Ben Roethlisberger’s Pittsburgh Steelers, setting a new Packers receiving record that had stood since Max McGee racked up 138 yards in Super Bowl I. Speaking of covers, Sports Illustrated ran a shot of Rodgers and Nelson doing an aerial shoulder-bump on the front of the mag in its postgame issue. I got lucky with Jordy, too. (I feel like I can call him by his first name because halfway through the 2008 season I drove to his tiny farm town of Leonardville, Kansas, and watched a Packers-Titans game on TV with his mom, friends, grandparents, Little League coach, high school chemistry teacher, and others, gathered in Nelson’s Landing, a sports bar Jordy’s parents, farmers by day, had opened in town.)

Nelson was a rookie that year, the Packers’ first pick in the draft. I devoted a chapter to him. He could have sucked. A lot of Cheeseheads and national prognosticators more or less predicted him to suck, or be average at best. I had some doubts myself. But “the Hick from the Sticks,” as an unkind Great Plains football writer once called him during his record-smashing Kansas State career, has ended up kicking total ass as a Green Bay Packer.

But I’m stupid in my book, too. I basically called Alex Smith — the quarterback who went No. 1 in the 2005 draft, 23 spots ahead of Rodgers — a bust. Except then in 2011 Smith led the 49ers to a divisional crown and their first conference championship appearance since 1997. After being traded to the Kansas City Chiefs in 2013, he led KC to a playoff appearance and was elected to his first Pro Bowl. In 2015, Smith spearheaded the Chiefs’ 11-game winning streak and their first playoff victory since 1994.

And in 2017? He started the season throwing four touchdowns for 368 yards as the Chiefs stomped the defending Super Bowl champion New England Patriots 42-27.

But life comes at you fast in the NFL. As I write, Smith is coming off some bad games and the article-negging has begun. Is the Alex Smith Era Over? one of them asks.

And that’s the point. The National Football League is an up-and-down experience for most players, and the quarterback position especially is a freakin’ yo-yo.

And the year of our lord 2017? It was like God himself was handling that yo-yo, spooling it out, reeling it up, snap, snap, snap, with a revolving lineup of QBs pinned to the toy. The aforementioned Roethlisberger? On October 8, he became only the seventh quarterback in 20 years to throw five interceptions and no touchdowns in a game. He posted a hideous 37.8 quarterback rating. And Pittsburgh lost to Jacksonville 30-9.

“Maybe I don’t have it anymore,” Big Ben said after the game.

One reporter present said Roethlisberger was being sarcastic. Others contended the Steelers stalwart truly did seem shaken by self-doubt. At any rate, it was a moot point — because Big Ben began dominating again, and the Steelers piled up Ws.

Outhouse to the penthouse (heh). Case Keenum knows all about that journey. Collegiate superstar. Undrafted in 2012. Signed by the Texans. Waived by the Texans. Signed by the Rams. Waived by the Rams. More address shuttling. Back with the Rams, he posted a perfect 158 rating in a 2015 game. He was benched the next year. Became a Viking in 2017. Took over after Sam Bradford went down. And all Keenum did then was rip off that “journeyman” sign and lead streaking Minnesota to six straight wins.

His last victory as this issue goes to press? Against his old team, the L.A. Rams. The QB nobody wanted beat the guy who replaced him, wunderkind Jared Goff.

And did I mention that on this same football weekend the Buffalo Bills benched their starting quarterback of the past couple seasons, Tyrod Taylor, went with rookie Nathan Peterman, and the newbie promptly threw four picks in 18 minutes, and a fifth INT for good measure just before halftime? Taylor was back taking snaps by quarter three.

It’s one of the worst signal-caller debuts in NFL history.

Nobody knows anything. Screenwriter William Goldman once wrote that about Hollywood. It can sometimes seem the same way with judging quarterback talent. Brock Osweiler, anyone? Arguably the most quarterback-starved team in league annals, the Cleveland Browns passed on Carson Wentz when they could have picked him in 2016.

And now Wentz, playing for the Philadelphia Eagles, looks like the next Tom Brady. Or the next Aaron Rodgers. But of course I might regret typing this. Or not.