by Tom Swift

Be careful whom you associate with. It is human to imitate the habits of those with whom we interact. We inadvertently adopt their interests, their opinions, their values, and their habit of interpreting events. Though many people mean well, they can just the same have deleterious influence on you because they are undisciplined about what is worthy and what isn’t. … Be selective about whom you take on as friends, colleagues, and neighbors. All of these people can have an effect on your destiny. The world is full of agreeable and talented folk. The key is to keep company only with people who uplift you, whose presence calls forth your best. But remember that our moral influence is a two-way street, and we should thus make sure by our own thoughts, words, and deeds to be a positive influence on those we deal with.

-Epictetus, Manual for Living (1994, Sharon Lebell translation)