There’s a well-worn saying that applies to many experiences in life: You’ll always remember your first time.

For five key Giants rookies who made their respective NFL debuts in Sunday night’s 40-0 loss to the Cowboys, they’ll never forget their first NFL game — and for all the wrong reasons.

The rookies’ nightmare began with center John Michael Schmitz rolling a shotgun snap to quarterback Daniel Jones on a third-and-7 from the Dallas 13-yard line on the Giants’ first offensive possession of the season.

Jones dove on the ball for a 14-yard loss that left kicker Graham Gano with a 45-yard field-goal attempt that was blocked.

“I take full responsibility for it,’’ Schmitz said. “The circumstances, the [wet] weather shouldn’t dictate my behavior, it shouldn’t dictate the snap at all. It’s on me. I’ve got to do a better job of executing and taking care of the ball. If you don’t do those things, you’re not going to win the game.

“All losses sting. You let it sit there for a while and you learn from it and you respond and move on to the next week.’’

On the second play of the second quarter, Giants rookie cornerback Tre Hawkins, a sixth-round draft-pick find the team is excited about, was called for a 37-yard pass interference penalty on a Dallas third-and-12.

Hawkins, a starter, interfered with Dallas veteran receiver Brandin Cooks on what was an incompletion that would have ended the possession.

The Cowboys, with the penalty moving the ball from their own 18 yard-line to the 45, led to a field goal that gave Dallas a 19-0 lead.

Starting cornerback Deonte Banks, the Giants’ top draft pick, didn’t have any poor, costly plays, but he did suffer some cramping in both legs to knock him out of the game.

Ironically, Banks came out of the game after breaking up a pass.

“We had a bad night,’’ Banks said. “I feel like I had an OK night. We’ll bounce back next week.’’

Asked what he’ll remember out of his NFL debut, Banks said: “I really don’t want to remember anything. Regardless of how I feel like I played, we had a bad night as a whole.’’

Jalin Hyatt, the speedster receiver the Giants drafted in the third round, had his forgettable moment as well, dropping a pass (his first NFL target) late in the third quarter that would have given the team a gain of about 16 yards and a first down.

Giants veteran running back and team captain Saquon Barkley was asked what his message would be for the rookies.

“It’s the National Football League,’’ Barkley said. “You’ve got to move on. The train’s going to keep on moving. Hop on. They’re talented.

“I told them [the rookies] all before — ‘You prepare for this moment your whole life, you’re going to have bad plays and you’re going to have bad games in the NFL. It happens to all of us. Continue to move on, learn from it and grow.’’’