That feeling of inevitably was starting to creep in for Keith Hernandez.

The dog days of August and a meaningless September seemed upon the Mets again, sitting 10 games under .500 with seemingly every National League team north of Miami between them and a wild-card spot.

“To be honest with you, I never would have thought this would’ve happened,” the SNY analyst said. “I still have lessons to learn, I was skeptical. … This is really a good lesson that you just never know in this game.”

“This” is a stunning Mets run that has seen them win 13 of their past 14 games to catapult to the forefront of the wild-card race with the Nationals, one of the teams left to chase, coming to Citi Field on Friday for a three-game series.

When this streak was four days old and apprehension still high, the Mets did something strange. The sellers became buyers and acquired Blue Jays ace Marcus Stroman.

“I strongly believe that if [general manager] Brodie [Van Wagenen] had a big selloff, that would have been the absolute wrong message to send to this team and that clubhouse with a lot of young players who are going to be here for a while.,” Hernandez said. “That’s [Pete] Alonso, that’s [Amed] Rosario, that’s [Jeff] McNeil, [Brandon] Nimmo.

“Now Nimmo has been around a bit and has had a taste of a lot of bad seasons, a lot of losing. They are like the little kid on the block to the Yankees. It is a lot to overcome in that clubhouse. If the Mets had sold, the team would’ve gone right in the tank. It’d be management’s quitting and here we go again. Brodie went out and put the Mets all-in and the team has responded. From a psychological point of view it was the best thing that happened.”

Stroman — followed by Noah Syndergaard and Jacob deGrom — will get the start Friday night as the JV part of the schedule ends. Stroman’s first Mets start was a struggle, as he allowed three runs over a laborious 4¹/₃ innings in Pittsburgh.

But, for Hernandez, the Mets have already accomplished perhaps the most important thing.

“No matter what Stroman does, no matter what the Mets do the rest of the season, this is a big learning lesson for the young kids who are going to be here,” the former first baseman said.

Alonso, McNeil and Michael Conforto are the first names that come to mind when you think of the Mets’ lineup youth movement. However, Hernandez said he believes the growth of Rosario should not be overlooked.

“It started last year with running out ground balls, and ever since, he hustles down that baseline,” Hernandez said. “He’s always looking to get that extra base, playing with energy, and it’s really lifted his game. He has been a big part of this surge. He’s a big component to all this.”