...and yet, some players do it very well. It's called plate discipline and it's what separates the good from the great.
There's no question that plate discipline separates the good from the great.
But it's a skill, a matter of ability, just like running fast or hitting for power or throwing a good curveball.
It's wrong to represent the issue as merely a matter of patience. Players can't suddenly begin laying off a low and away slider any more than they can begin hitting more home runs.
Changing your approach at the plate isn't something that can be changed simply by wanting to. Players can improve, just as they can improve the routes they take to fly balls or their ability to keep a fastball low in the zone, but a hitter with a poor approach can't just develop a good approach because a coach explains to them the value of a walk, or the value of being selective. Just like no amount of explanation of the difference in positional value between 1B and 2B can make Prince Fielder a middle infielder.