Before considering the capacities needed for this definite practice, let us run over the obstacles to Yoga as laid down by Patanjali.
The obstacles to Yoga are very inclusive. First, disease: if you are diseased you cannot practice Yoga; it demands sound health, for the physical strain entailed by it is great. Then languor of mind: you must be alert, energetic, in your thought. Then doubt: you must have decision of will, must be able to make up your mind. Then carelessness: this is one of the greatest difficulties with beginners; they read a thing carelessly, they are inaccurate. Sloth: a lazy man cannot be a Yogi; one who is inert, who lacks the power and the will to exert himself; how shall he make the desperate exertions wanted along this line? The next, worldly-mindedness, is obviously an obstacle. Mistaken ideas is another great obstacle, thinking wrongly about things. One of the great qualifications for Yoga is “right notion”. “Right notion” means that the thought shall correspond with the outside truth; that a man shall he fundamentally true, so that his thought corresponds to fact; unless there is truth in a man, Yoga is for him impossible. Missing the point, illogical, stupid, making the important, unimportant and vice versa. Lastly, instability: which makes Yoga impossible, and even a small amount of which makes Yoga futile; the unstable man cannot be a yogi.