The best way of keeping the mind free from all undesirable impressions is not to partake them at the moment when they fall upon the mind. For instance, if someone is disagreeable, instantly his influence produces the same thing in another person with whom he is disagreeable. The best way to avoid it would be to stand on one's guard that one may not catch his infectious disagreeableness. All such things as pride, prejudice, jealousy, intolerance, coldness, have a great influence upon a person.