Coaches often tell their players "act like you have been there before." It is a core principle of sportsmanship and maturity.
Junior Lake's show boating a home run when his team is down 6-2 was selfish bush league. It angered the Marlins players to the point that both benches cleared to vent.
Coaches cringe when a wide receiver catches a touchdown pass with 17 seconds to play, then does a victory dance in the end zone - - - when his team is still down by 28 points. Garbage points don't get celebrations.
The NFL ("No Fun League") has penalized excessive celebrations on the field because, frankly, it was getting extremely stupid and demeaning to the image of the sport. You can give off the swagger of a champion by catching your touchdown pass, and handing the ball to the back judge while you are walking off the field. What is a more powerful message to your opponent after scoring than "that's was no big deal."
Lake is getting an opportunity to play more with Jorge Soler's ankle injury. But Joe Maddon needs to keep his young players in check. Hot dogging, show boating and being unprofessional are elements that lead to bad habits in the clubhouse. A disciplinarian coach would have sat Lake for the rest of the game to send a clear message.
In hockey, Coach Q does that all the time. If one of his Blackhawk players screws up on the ice or does something stupid (like a bad penalty), he will sit the player for long stretches. That hurts the club because it means the other members of the team have to make up someone else's dumb mistakes. In the locker room, team leaders like Toews, can then police the roster and get everyone back on the same page. That is the maturity level that teams strive for when they want to win championships. The Blackhawks are a team solely focused on winning another Stanley Cup.
The Cubs are looking for maturity through leaders like Anthony Rizzo. But he seems to be a mild manner, quiet guy. But quiet guys, including Jon Lester, can lead by example. Maybe later on someone else, like Kris Bryant, will take the reigns and become the captain of the team.