That's true. But it's more meaningful from the societal level than the personal. As an individual looking for interesting or useful things you don't already know it's usually far more efficient to read a few books than to spend the same amount of time getting to know people outside your circle.

Now if you want to learn something that a large number of people don't already know then goes treasure hunting. But, suggesting people need to talk with a wide range of people to grow as a person is simply untrue.