Grab a hold of Tarik Cohen while you still can. (Tannen Maury/European Pressphoto Agency)

It happens every year: We spend August fine-tuning our notions of what the forthcoming NFL season will look like, and then a single weekend reveals our hubris.

The NFL is undefeated in exactly one way: Unlike every other major American sport, it completely reinvents itself every year. Matchups people told you would be cake suddenly look challenging. Offenses that were suppose to stink show signs of extreme improvement. Players labeled as worthless suddenly produce.

And now comes the adjustment period. You drafted your fantasy team as best you could with the information you had, and now we all have to dance delicately: figure out where our assumptions were flawed, try not to overreact one week into the 2017 season, and make the right adjustments. It’s difficult, but it’s really fun. And it’s why this week I’ll focus on waiver additions more than starts and sits:

Must-Add: Tarik Cohen, RB, Chicago Bears

They don’t call him the Human Joystick for nothing. Cohen was a complete blast against the Falcons. He’s 5-foot-6, so he’s never going to be an every-down back, but he’s already one of the NFL’s quickest players and he nearly caught a long TD pass to go with his short receiving score. Heck, he took a wildcat snap and handed it off to Jordan Howard on Howard’s TD run! After that debut, which was filled with legit jaw-dropping moments of quickness — and in which, admittedly, he had more receptions than carries — the Bears have decided they’ve found their Darren Sproles. That makes Cohen a candidate for 120 or 130 touches and 800 total yards: not must-start territory, but perfect as a kicky PPR flex.

Must-Start: Todd Gurley, RB, Los Angeles Rams

You’re going to hear grouchy fantasy football people whinging about Gurley: He’s been held to fewer than 80 rushing yards in 16 of his past 17 games and hasn’t had a 100-yard rushing day since December 2015. But I have more faith in new Rams Coach Sean McVay than I did Jeff Fisher. When I watch Gurley’s tape from Sunday, I see his first several carries go right up the gut, right where they’ve always gone, and get stuffed. But then I see McVay make adjustments. Some sweeps. Some pitches. And some screens! By golly, yes, the man can actually catch the ball. And when Gurley got in the open field, he looked like the playmaker I remember from his rookie year: a big, fast, shifty monster. The Rams’ offensive line still has miles to go, but McVay is going to be smarter using Gurley.

Must-Add: Kenny Golladay, WR, Detroit Lions

Golladay scored twice in Detroit’s comeback win against the Cardinals, after spending August being hyped as “Minitron.” I don’t know that I consider him a must-start just yet. Golden Tate is the axis around which the Lions’ passing offense turns, and in Week 1 the deeper passes were split among Golladay, Marvin Jones and T.J. Jones. Both Golladay and Marvin Jones have the look of red-zone jump-ball weapons, so there could be some weekly back and forth (in fact, Jones caught Detroit’s first TD pass on a short throw). But it was Golladay’s second touchdown — a beautiful, well-defended, diving catch on which he snagged the ball off the turf — that caught my attention. Add him, stash him and let’s see how he does Monday night against the Giants.

Must-Sit: DeShone Kizer, QB, Cleveland Browns

If you’re someone who streams QBs, you might be tempted by how professional Kizer looked in his rookie debut: 222 passing yards, a TD throw and a rushing TD with one interception. Week 2 is a poor one for matchups among lightly owned fantasy QBs, so you may be turning your eyes toward Kizer as a safe source of running-based points. I wouldn’t do it. I came into 2017 with questions about the Ravens’ front seven, but they looked devastating against the Bengals and turned over Andy Dalton five times. If stream you must, I’d be looking at the likes of Alex Smith against the Eagles or Sam Bradford against the Steelers.

Must-Add: Kerwynn Williams, RB, Arizona Cardinals

Here’s the part where we sort through the rubble of many folks’ No. 1 overall pick in fantasy football this year. David Johnson seems destined for injured reserve after taking a big hit on his wrist Sunday, which means he will miss most (if not all) of the 2017 season. It’s a crusher made worse by the fact that the Cardinals have no good replacement. Williams is DJ’s direct backup, and for the final quarter Sunday, he saw the most time lined up in Arizona’s backfield (and he scored from the Lions’ 3-yard line the play following Johnson’s injury). But Williams is a journeyman who has never exceeded 53 carries in a season and is 5-8 and 198 pounds. Andre Ellington also resides on this depth chart, but the Cardinals tried converting him to a wideout this summer, and he’s several leg injuries removed from his peak quickness. Arizona also signed D.J. Foster off New England’s practice squad and could re-sign veteran Chris Johnson, but if I’m taking a single shot on any replacement, I guess it would be Williams. The Cards play the Colts on Sunday; if Week 1 was any indication, some TDs figure to be available.

Christopher Harris runs HarrisFootball.com, where you can find more info on the “Harris Football Podcast,” with new episodes every weekday.)