The mind is the friend of one who has conquered the mind.

Meditation Yoga

Chapter 6, Verse 6

ndhur-ātmā’tmanas tasya

yenātmaivātmanā jitaḥ

anātmanastu śatrutve

vartetātmaiva śatruvat

The mind is the friend of one who has conquered the mind. But for one whose mind is uncontrolled, the mind remains hostile, like an adversary.

So again, Lord Krishna keeps repeating in different ways that one who has conquered the body, and the senses, whose mind is always focused and fully under control, easily redeems himself from worldly existence and attains God-Realisation. Whereas the “…one whose mind is uncontrolled, the mind, remains hostile, like an adversary.” In this state, one is a slave to the mind, the senses and the body. It’s like a person who is sick, because he has lots of poison inside him. These people do everything to oppose their own spiritual growth, because of egoism, sense of possession, attraction and repulsion, lust, anger, and greed: they fall victim to these sinful acts due to the mind. They become their own adversary.

Nobody can make you unhappy, but yourself. The cause of your happiness doesn’t lie in somebody else, but in you! If you want to be happy, you are happy. And if you want to be sad, you are sad. Very often people say, “I feel very sad, because you have not given me attention.” This is an example of an uncontrolled mind and stupidity. One should face the truth, which is, “I feel sad, but I don’t want to change anything! I am just enjoying feeling sad, because this person has not looked at me and doesn’t pay any attention to me.” You see this happen in daily life, don’t you? Due to this, people become the source of their own misery. Whereas when one doesn’t expect anything, one is free and develops true happiness.

If you change the mind, if you train the mind to see in a different way, in a positive way, then you will be happy. You will not be miserable. You will not be attached. That’s why the song says, Jiv Jago, Jiv Jago Gorachandra Bole: “Awake, human, awake!”

Bhagavad Gita