Learning and practicing yoga is not about enhancing one's physical and mental condition and ability to be able to perform the yoga asana poses and exercises or some other kinds of physical and mental activities in life, to be empowering or boosting the sense of self-esteem, self-worth, confidence, achievement, goodness or meaningfulness, being motivated and encouraged by the yoga teachers to keep practicing regardless of failures/challenges/difficulties, in order to experience the physical and mental transformation from being not strong and flexible or bold enough to perform certain yoga poses/practices until they are strong and flexible or bold enough to be performing those yoga poses/practices, to let them know that it's possible for them to do and achieve anything that they want, if they are being determined and persevered, and never give up.
There's nothing wrong with that, in fact it's a very good motivational training workshop just like many other motivational workshops in the world for people to develop certain degrees of physical and mental strength, flexibility and stamina, as well as the skill, in order to be doing something and achieving certain results, however, yoga and its practice, which is the elimination of ignorance and egoism, the annihilation of the modification of the mind, as well as the realization of Selflessness, is nothing to do with the enhanced physical and mental condition and ability to be doing and achieving something either in everyday life or in the yoga practice.
It's very good for the motivational teacher/trainer to give positive encouragement and acknowledgement towards the students/trainees in any kind of motivational workshops, by cheering, "Well done!", "Yes! You can do it!", "Keep it up!", "Very good!", "Believe in yourself!", "Never give up!", "Yeah! You done it!", and so on, but again, the continuous improvement of the physical and mental ability and achievement of the students of yoga doesn't determine the elimination of ignorance and egoism, the annihilation of the modification of the mind, or the realization of Selflessness. In fact all these motivational workshops are only strengthening the idea of 'I' and empowering egoism of attachment, identification, desire of craving and aversion, comparison, judgment and expectation towards the qualities of names and forms.
Even if the yoga students are unable to perform many kinds of physical or mental activities, not to say, any of the yoga asana poses or breathing exercises, due to some physical and mental limitation and disability or environmental restriction, they still can practice yoga to be eliminating ignorance and egoism, disciplining the outgoing tendency of the mind, quieting the restless state of the mind, purifying the intellect, performing self-inquiry, realizing the truth of selflessness and impermanence, be free from ignorance and suffering, and resting in unconditional peace, if they know how to eliminate ignorance and egoism.
It's not about "Nothing is impossible," but "Non-attachment towards both possibility and impossibility."
By developing strong determination and perseverance to be performing many different kinds of actions or yoga practices, with the great aspiration, positive thinking and optimism to be 'achieving' something, but without knowing how to let go attachment, identification and the desire of craving and aversion towards goodness/badness, positiveness/negativeness, meaningfulness/meaninglessness, righteousness/wrongfulness, and etc, it doesn't lead the mind towards Selflessness, or liberation from ignorance and suffering.
That's why there were/are many great competitive sports persons, or world champions, or scientists, or geniuses, or creative artists, in the past or in the present, were/are not necessarily be free from ignorance and egoism or painful sorrow and suffering with their superhuman physical and mental ability and achievement, unless they realized Selflessness, knowing what is 'I', and be able to let go or unattached towards whatever the mind perceived through the senses.
Because yoga is not about how many actions that the body and mind can perform, or how many things that the body and mind can achieve through developing and enhancing physical and mental condition and ability, it's about letting go the attachment, identification and desire of craving and aversion towards what the body and mind can do and cannot do, achieve and doesn't achieve, as well as all kinds of impermanent qualities of names and forms.
Siddhartha Gautama Buddha, or any serious selfless yoga teachers that teach about yoga as it is that leads the mind towards the annihilation of ignorance and egoism, couldn't/didn't/don't say to the practitioners, "Very good! Keep it up! You can do it! I can, so can you! Believe in yourself! You are incredible superhuman!" when they were/are performing or not performing any kind of actions/practices, regardless of whether they were/are doing it right and improving, or not, or "Yeah! Well done! You are liberated now! Great job! I'm so proud of you! You should be so proud of yourself! And your country and all your family and friends will be very proud of you!" or issued them an 'internationally recognized certification' sanctioned by and affiliated to '..xxx..', when they attained/attain certain realization.
Inquire towards the truth of everything.