Kirk Cousins threw three interceptions but also recorded enough passing yards to surpass 4,000 for a third straight season. (Toni L. Sandys/The Washington Post)

In the last game of his most taxing season, Kirk Cousins was a dud. The Washington Redskins quarterback, overanalyzed even by the position’s standard, couldn’t lift his team to mediocrity anymore. Heck, he could barely convert a first down.

It wasn’t just his worst game of the season; it was the worst of his 57 career starts. Never has he endured this wretched a trifecta of low production, high turnovers and poor efficiency. Late in the season, as Washington scraped together the vigor to keep from collapsing, you saw the value of Cousins’s stable and effective style. On Sunday at frigid MetLife Stadium, you saw nothing from him. Nothing good. So Washington’s season ended with an 18-10 loss to the New York Giants, a bitter result that halted the team’s happy dance toward an 8-8 record and left the never-ending Cousins contract saga with a bad final memory of 2017.

If the Cousins supporters were toasting his three-touchdown performance last week against Denver in what could have been his last home game at FedEx Field, then his detractors are ordering champagne now. It’s a vicious cycle that the franchise perpetuates with its indecision and lack of creativity in negotiating with Cousins. For the better part of three seasons — 48 games — Cousins has been playing for his future, having his worth scrutinized with every performance.

It needs to stop, mostly for our sanity. The experience is so unhealthy that truthful and balanced evaluation gets washed away by the hyperbole leaking from both sides. His highs have become asinine “Told ya so!” material. His lows have become embarrassing “You like that!” taunts. A fair contract proposal seems like the most intricate puzzle ever created. Maybe that’s because we’re all dumber for going through this debacle.

It can’t just be that Cousins is a good quarterback who played a terrible game Sunday. There must be some mystery about him that the performance exposed, some proof — See! See! See! — that he is unworthy of whatever big payday he will receive. This bad taste will linger into the offseason and influence Washington’s simple-minded decision-making in some way, just like the disappointment of missing the playoffs in the last game of 2016 colored the franchise’s thinking.

In the previous two games, in victories over Arizona and Denver, the story line became the importance of a competent starting quarterback. Cousins was good in those games, his counterparts were terrible, and it was easy to declare, “Would you rather have a quarterback who can play? Or would you rather be searching like those poor losers?”

Now comes the other side. Cousins completed only 20 of 37 passes for 158 yards. He threw three interceptions, one of which led to a Giants touchdown. He hadn’t thrown three picks in a game since Oct. 12, 2014. His 31.1 passer rating was the worst of his 57 career starts. His 158 yards were the third fewest of his career. He ran for Washington’s only touchdown, but he didn’t throw a touchdown pass for only the sixth time as a starter.

“It wasn’t good,” Coach Jay Gruden said when asked about Cousins’s performance. “Nobody on offense played good. I called the plays, and I was awful. So anytime you have a performance like this, it’s just not good by anybody, unfortunately.”

Gruden’s offense gained just 197 yards and finished with only one third-down conversion in 13 attempts. It took the 3-13 Giants just 2:18 to score enough points to win. New York running back Orleans Darkwa ran for a 75-yard touchdown on the Giants’ second play, part of Darkwa’s 154-yard effort and 260 rushing yards for the team. On the ensuing drive, Cousins threw an interception to linebacker Kelvin Sheppard on third down, giving the Giants the ball 19 yards from the end zone. After Eli Manning threw a touchdown pass to Hunter Sharp, New York led 12-0.

During this span, Washington also lost starting running back Samaje Perine to an ankle injury, and Ty Nsekhe — Trent Williams’s replacement at left tackle — went down with a knee injury. The game was all but over, unless Cousins could make something out of nothing.

Once considered merely a system quarterback, Cousins has grown in his ability to elevate an undermanned team. He has willed the team to several victories, including road wins over Seattle and the Los Angeles Rams. On Sunday, he surpassed 4,000 passing yards for the third straight season, the first quarterback to do so in franchise history. His numbers — 4,093 yards, 27 touchdowns, 13 interceptions, 93.9 passer rating — amount to a very rewarding season after you consider all the injuries and personnel miscalculations that contributed to the offense’s struggles.

Cousins gave this feeble offense a chance most every game. Sunday was so startling because, even if you don’t value Cousins’s talent as much as others, it’s rare for him to be so ineffective. He overthrew some passes and underthrew others. At times, he was too aggressive and forced the issue. He couldn’t drop back and throw the ball without being hounded by the Giants’ pass rush. He didn’t even show his usual touch on short passes.

“The fact of the matter was we never really got it going,” Cousins said. “A combination of reasons, but I was really disappointed with the fact that we never really found a rhythm and couldn’t really get going.”

Since taking over for Robert Griffin III as the full-time starting quarterback, Cousins has played 48 games. The stats suggest this is a once-in-48 clunker. It happens to every quarterback. In the big picture, it doesn’t mean much to how Cousins is evaluated. Cousins continues to evolve, but there aren’t any major revelations left. He’s an efficient, productive quarterback who is ideal for a balanced football team. As he proved this season, he’s more comfortable carrying heavier responsibility than he used to be, and perhaps that makes Washington more amenable to offering him a long-term deal with a guarantee in the $80 million range.

After placing the franchise tag on Cousins for two straight seasons, Washington is faced again with the same offseason issue: It needs to develop the guts, either to offer Cousins can’t-say-no money or to let him go for whatever return it can salvage. At this point, it’s possible that freedom is most valuable to both sides. Cousins is just as reticent to commit. And Washington has gone 9-7, 8-7-1 and now 7-9 in the past three seasons. The franchise isn’t a disaster right now, and Cousins has been a huge part of that. But with a 24-23-1 record over three seasons with Cousins as a starter, it’s clear this team is stuck on average, and is it possible to get beyond that while retaining Cousins at what would have to be a record-setting price?

That’s the question. It’s a nuanced, vexing question since Washington failed to sign him when his value was lower. It’s not, “Cousins threw for 300 yards! Is $30 million a year enough?” And it’s certainly not, “Cousins threw three picks. Can we trade him for better turf at FedEx?”

“We have to have stability at that position, somehow, some way,” Gruden said.

With 2017 in the recycling bin, the onerous search for somehow and some way starts again.

For more by Jerry Brewer, visit washingtonpost.com/brewer.