In plain words
Einstein too once said of this, 'Tell me your company I shall tell you what you are'. Whatever company you keep, that very nature you too will take on. That is why, in Vedānta:
Satsaṅgatvē nissaṅgatvaṃ nissaṅgatvē nirmōhatvaṃ nirmōhatvē niścala tatvaṃ niścala tatvē jīvanmuktiḥ.
Satsaṅga is most necessary for man.
And the fourth is vipralipsa. Vipralipsa means envy. This envy is a very bad quality. It cannot bear to see those who have. When it sees a man of wealth, it is scorched without any burning. It is forever searching out nothing but the faults of others. It wishes others nothing but harm. It never thinks of the good. 'Brahmavit brahmaiva bhavati': as its thoughts are, such is the form it takes on. This envy turns man into a demon. For man this envy is a fault that brings great sin. All these faults, every one of them, enter upon the Manas. Though the Manas is good, through this contact the Manas becomes impure.
So Vedānta teaches us to put away mala, āvaraṇa and vikṣepa. This impurity is just like excrement. No one at all desires excrement with fondness, and no one keeps it near. That is why an impure Manas reaches no one. A river, at the time of its birth, is born as utterly pure water. But by the time it comes down to the level of the people who use it, it becomes impure. In just the same way the stream of the Manas flowed pure. By the time it reaches the man who experiences it, it becomes impure. In the world people fall prey to many sorrows through this very envy alone. Bearing harsh envy, however much evil you wish them, you hand evil to the other, and that very evil turns back on yourself many times more than that. You all know the power of this envy in the Mahābhārata. However much envy the Kauravas felt on seeing the Pāṇḍavas, in the very end that envy turned and destroyed them themselves. It brought them to ruin. Through this envy anger grows. To one who has anger, humanness makes no sense at all.