The definition of insanity is doing the same thing again and again and expecting different results.

Well, the Giants are not insane ... except maybe where it matters most.

They made wholesale changes this offseason but stuck with quarterback Eli Manning for a franchise-record 16th season.

So will they make the playoffs for just the second time in the last eight seasons?

Here are six reasons they will not:

1. Empty sacks.

After finishing second-to-last in the NFL in sacks, a smart short-term plan for the Giants would have been to sign Preston Smith, Za’Darius Smith, Ziggy Ansah or one of the other top free-agent pass-rushers available.

Instead they took a bargain chance on Markus Golden — who had 12.5 sacks in 2016 but only 2.5 since and has been slow to recover from a torn ACL in 2017 — and traded sacks-leader Olivier Vernon for offensive line help (Kevin Zeitler). Golden is the only player on the roster with more than 6.5 career sacks.

The Giants tripled down on youth by elevating Lorenzo Carter to starter, drafting raw Oshane Ximines in the third round and trusting run-stuffing first-round pick Dexter Lawrence to be more of a pass-rusher than he was at Clemson.

Hard to believe it’s enough of an upgrade.

2. No way without OBJ.

Manning’s unwritten philosophy over the last five years: When in trouble, throw to Odell Beckham. That’s how you end up with 44 touchdowns in 59 career games.

For all the drama he caused on and off the field, Beckham was the bail-out button for the Giants. Throw him a quick slant and watch him go for a big gain. Throw into double coverage down field and watch him wrestle away the ball. Have him throw a pass to jumpstart the offense.

Golden Tate has four 90-catch seasons in his last five and Sterling Shepard is on the rise, but both work best out of the slot and underneath. Who is going to stretch the field and keep the safeties from cheating up on running back Saquon Barkley?

Don’t be fooled by the 25.5 points per game in the last four when Beckham was injured. They went 1-3 in those games, with a win over a quitting Redskins defense, a shutout loss and two failed last-minute drives by an offense that scored until it mattered most.

3. Name those cornerbacks.

Janoris Jenkins is two years removed from his only Pro Bowl season but still has playmaking ability when his head is in the game.

He has more games played (100) and starts (96) than all the other cornerbacks combined — and that’s if veteran Tony Lippett makes the team. Without Lippet, it’s a blowout.

Grant Haley, Sam Beal, DeAndre Baker, Julian Love and Antonio Hamilton have a combined 35 career games played — all belonging to Haley and Hamilton, who mostly are valued for special teams.

It’s a passing league, especially with way defensive pass interference is called. The downside of relying on so much youth is the potential for miscommunications, blown coverages and open receivers streaking toward the end zone.

Do the Giants have enough firepower to win shootouts?

4. Manning’s decline.

Manning completed a career-high 66 percent of his passes and threw his fewest interceptions (11) since 2008. But those numbers mask his year-over-year decline, as is expected from a 38-year-old quarterback.

Since 2013, Manning ranks No. 27 out of 31 in quarterback rating among passers with at least 40 starts, ahead of only Ryan Fitzpatrick, Case Keenum, Blake Bortles and Joe Flacco. His air yards per attempt, touchdown passes per attempt and yards per completion all are on the steady decline.

Perhaps the most troublesome sign is that years of collapsing protection around the edges and in his face combined with his sense of self-preservation appear to be making the durable Manning more susceptible than ever to sacks. He used to prolong plays with his sneaky pocket mobility, but now he curls up a fraction of a second sooner, as if bracing for the worst.

Giants general manager Dave Gettleman isn’t fond of analytics, but a telling number is Defense-adjusted Value Over Average (DVOA). The last time Manning’s season-long score was positive was in 2014.

5. Too big of a jump to make.

It seems every year one or more teams go from a last-place division finish to the playoffs.

The Giants are tied for a NFL-high 24 losses over the last two seasons and are 20 games under .500 (38-58) over the last six seasons combined, even with an 11-5 record mixed in.

The proud Giants don’t want to admit this truth usually reserved for the Browns, but they have been one of the worst on-field products in the NFL for a long time. Pro Football Focus lists the Giants as having the No. 27 most-talented roster in the NFL.

The Bills and Dolphins once were great and have been mired in a two-decade slog. Are the Giants headed there? If the Eagles develop into the dominant NFC East team behind Carson Wentz, it’s into the wild-card jumble at best.

Giants coach Pat Shurmur’s career record is 15-34, including two seasons with the Browns and one game with the Eagles.

6. Daniel Jones distraction.

The Giants built a locker room with chemistry to withstand distractions.

But Manning himself admitted things like a player’s uncertain future can become a “hassle” when the questions are the same weekly.

Jones will be lurking around the corner like the 600-pound elephant in the room. Every loss means he is closer to taking over.

What if teammates realize during practice the rookie Jones gives the team a better chance to win than Manning but management is reluctant to pull the plug? That is when trouble brews.

Once Jones takes over as the starter, write off the playoffs. Only 17 rookie quarterbacks have started a playoff game since 1983.

Ryan Dunleavy may be reached at rdunleavy@njadvancemedia.com. Follow him on Twitter @rydunleavy. Find our Giants coverage on Facebook.