Hi Navegante,
This is piece of advice. By observing the friends who associate with this person, we can infer about his or her character.
Example:
A man is known by the company he keeps -- just look at how uncouth his friends are!
You have a part to play for the judge's unfavourable impression of you -- one is known by the company one keeps.
Just as a side discussion, the proverb "Birds of a feather flock together" also advises us that people of similar tastes, interests and characters usually spend time in each other's company.
Hope this helps.
Cheers,
Lance