The company you keep is important. If you leave your coat in a room where people are smoking, pretty soon it will smell of smoke. If you leave it outside in the garden, later on, when you bring it indoors, it will carry with it the fragrance of fresh air and flowers.
Such is the case with the mind. Your garment of thoughts absorbs the vibrations of those with whom you mix. If you mingle with pessimists, in time you will become a pessimist. And if you mingle with cheerful, happy people, you yourself will develop a cheerful, happy nature.
Environment is stronger than will power. To mix with worldly people without absorbing at least some of their worldliness requires great spiritual strength.
Beginners on the spiritual path, especially, should be very careful in the company they keep. They should mix with other devotees, and try not to mingle with ego-saturated, worldly people. They should especially avoid people who are negative, even if those people are devotees.
Whether one becomes a saint or a sinner is to a great extent determined by the company he keeps.
— The Essence of Self-Realization