SAN DIEGO — When a young player gets called to the majors there are many lessons to be learned. Look at the progress Clint Frazier has made with the Yankees, picking up a vital batting tip and also learning how to act more like a major leaguer.

It’s not just about the playing time for young players.
It’s about the little things. Young players can observe so much and be better prepared for the future.

The Mets beat the pitiful Padres, 6-5 Tuesday night at Petco Park thanks to a two-run checked-swing Little League home run to right by Yoenis Cespedes in the seventh and yet another Padres critical error, a wild throw on the relay by first baseman Wil Myers.

The Padres had time to play Frisbee football in the outfield before the game but no time to work on cutoffs. So it goes in 2017.

The Mets have opted to take the glacier approach with shortstop Amed Rosario, who has had to deal with a stomach illness that recently sent him to the hospital.

Maybe he is just sick of being in Las Vegas.

This West Coast road trip is another opportunity the Mets are not taking full advantage of because it would have been nice to have Rosario around just to soak up information — instead of sending a tweet a litle over a week ago that did not go over all that well in the Mets’ clubhouse.

Rosario’s bended-knee proposal tweet shows that the personable young player still has a bit of growing up to do. That’s fine. Rosario is just 21. Just imagine if Frazier, 22, had sent such a tweet.

“Amed is ready,’’ he wrote.

Yes he is, but the Mets are not.

Rosario will be up at some point but because the Mets are going nowhere why not get Rosario up here and learning a week ago?

His talent would not hurt, either.

The Padres tied the game 4-4 in the fifth when Matt Szczur beat out a hit to short and then Carlos Asuaje hit a little bouncer to third that Asdrubal Cabrera muffed. Two batters later a sacrifice fly tied it until Cespedes’ Little League home run.

Spending time around this team, even if there is a disgruntled player such as Cabrera would not harm Rosario, yet another excuse in the litany of excuses the Mets have put forth on why Rosario remains in Vegas.

Cabrera’s reaction after having to move from shortstop to second is understandable because of the pride he has in his job. No one in any line of work is happy with what they view as a demotion, and it would not hurt Rosario one bit to see that.

The Mets have opted to put Rosario in this baseball bubble. When he does arrive he will become the ultimate center of attention.

Sure, it’s not the end of the world that Rosario is in Vegas. What is lost though, are teaching moments and again, going back to Frazier, look how much better a player Frazier is today than the day he got called up.

If Frazier gets sent back down, the desire to return will make him work harder. It is these small, wrong decisions that can set back a franchise.

Jose Reyes is more than willing to mentor Rosario on the shortstop front and keeps in contact with Rosario, but his helpful advice would be even better on a game-by-game, play-by-play basis. Reyes could slide back to third base and be right alongside Rosario at short.

Not to mention that Rosario could help the Mets on the field. All along, the Mets would be helping Rosario grow as a player. All that is going to have to wait a little longer.

Meanwhile the New York team that is in playoff contention, the Yankees and their manager Joe Girardi are happy that Frazier came up and showed the ability to learn quickly.

That gamble paid off for the Yankees and Frazier.

You can be sure, too, Mets management is happy that Rosario has been kept down in Las Vegas.

That was the plan and they rarely deviate from the plan.