I watch a lot of MLB games and really, you can't apply what they do to youth baseball players. They are so physically gifted that they can do things that youth and high school players can't do and probably never will be able to do.
However we as coaches can teach the best players in the big league's mental approach to hitting because every age hitter can do that.
I've watched so many MLB games in my life and I finally realized the best players really don't want to swing at pitches early in the count unless it is in their preferred zone, which means there is a lot of swinging with 2 strikes. Then the foul balls begin and good hitters eventually get a pitch they can handle and hit it square. It takes a lot of discipline and confidence to take that approach, which all great hitters have.
MLB rookies, below average hitters and high school and youth players take the opposite approach for the most part. They are swinging early in the count and when they down in the count are mentally beaten because they expand their strike zone and swing at any pitch close. Smart and good pitchers will never throw strikes to players in this category, and their lack of discipline and fear leads to a lot of outs.
It is up to coaches to make hitters be patient and believe in themselves so they will still hit when behind in the count and not worry or internalize about what might happen. Take pitches confidently, understand hitting situations and visualize success.