The term Yoga has its verbal root 'Yuj,' in Sanskrit, which means "to join." Yoga derives from the same root as the English word 'Yoke', "to join." Yoga was systematized by a sage (sage = scientist + saint) called Patanjali, who, around 300 BC codified the teachings into 196 short aphorisms or sutras. Yoga-sutras of Patanjali is a great text of psychology. Patanjali had analyzed human mind in a very scientific fashion.
Patanjali described Yoga as 'control of mind and its modifications or thoughts'. The Bhagvad Gita says : 'Samatvam Yoga uchyate'. 'Evenness of mind is Yoga'.
The focal point of the above definitions is the mind. The developed mind is what distinguishes the humans from the rest of the species. The developed mind is a boon as well as a curse to the mankind. There are many metaphors used to describe the unsteady nature of our mind. The mind is like a monkey jumping from one branch to another, or like a wild bull difficult to tame.