The mind of an average person may be pictured as an unruly horse that jumps and kicks and throws anyone that tries to ride it. Masters of the world are those who have mastered themselves, and mastery lies in the control of the mind. If the mind became your obedient servant, the whole world is at your service.

~~~ "Githa Series II, Amaliyyat 1, Psychology ", by Hazrat Inayat Khan (unpublished)

He who does not direct his own mind lacks mastery. ... If there is any self of which one can say, 'This is man', it is the mind. The three Sanskrit words Mana, Manu, Manusha show that man is his mind, is the product of his mind, and is also the controller of the activity of mind. If he does not control his mind, he is not a master but a slave. It lies with his own mind whether he shall be master, or whether he shall be slave. He is slave when he neglects to be master; he is master if he cares to be master.
Mastery lies not merely in stilling the mind, but in directing it towards whatever point we desire, in allowing it to be active as far as we wish, in using it to fulfill our purpose, in causing it to be still when we want to still it. He who has come to this has created his heaven within himself; he has no need to wait for a heaven in the hereafter, for he has produced it within his own mind now.