Appreciating the Righteous Man
Bereishis, 28:10: "And Jacob departed from Beer Sheva and went to Haran."
Rashi, 28:10: sv. And Jacob departed: It only needed to say 'and Yaakov went to Haran', so why did it mention his departure? Rather it tells us that the departure of a righteous person from the place makes an impression; for when a righteous person is in a city, he is its magnificence, he is its splendor, he is its grandeur. Once he has departed from there, its magnificence has gone away, its splendor has gone away, its grandeur has gone away...
Rashi explains the seemingly repetitive language of the Torah in describing Jacob's departure from Beer Sheva. The Torah emphasizes this point to teach that the leaving of a tzaddik (righteous man) such as Jacob causes a great void. The Kli Yakar asks that this was not the first time that a tzaddik left a place - Abraham and Isaac also travelled in their lifetimes, so why does the Torah choose to teach this lesson only with the leaving of Jacob?(1)
The key to answering this question is to note that there was something unprecedented about this particular departure; it was the first time that a tzaddik left a place where other tzaddikim remained. When Abraham and Isaac travelled, there was nobody remaining who attained the level of 'tzaddik', whereas on this occasion, Isaac and Rebecca remained in Beer Sheva. How does this help answer our question? There are many people who do not appreciate the value of a tzaddik; this includes evildoers who actually despise the tzaddik and see him as an obstacle to preventing them from fulfilling their desires. Yet even people that are not evildoers do not recognize the true greatness of a tzaddik, accordingly they would not necessarily comprehend the scale of the less upon his departure. Only someone who is on a high level themselves can fully recognize the value of a tzaddik and the corresponding vacuum that is created on his parting. Therefore, the Torah only taught the lesson about the inestimable value of a tzaddik when other tzaddikim remained - the first time that this took place was when Yaakov left his parents.
One interesting lesson that can be derived from this explanation is that recognizing the qualities of a person is a quality in and of itself. A person with a highly developed sensitivity to positive traits will more eagerly seek them out and notice them in others. The obvious application of this is to strive to learn from the tzaddikim that are in their vicinity. This includes speaking to them as much as possible, but also simply observing their 'mundane' actions and speech. In this way one can derive great practical lessons about how to behave in a variety of life situations.
1. Kli Yakar, Bereishis, 28:10. See there for two answers. The answer given here is similar, though not identical, to his second answer.