The very mention of the word yoga conjures up images of a lean, taut figure sitting in absolute padmasana and complete meditation in my mind. Yes, indeed a Yogi is a term referring to anyone practicing yoga. Almost always there are some unwritten rules that Yogis follow from being strict disciplinarians of their regular schedules to practicing yoga at a proper time. Though voluntary, I believe these are some absolute ethical duties of a yogi. Some of the key ones include:
• Ahimsa: Practicing non-violence in eating and regular work
• Satya: Sticking to the principles of honesty, avoiding falsehood
• Daya: Compassion
• Avoid stealing of any type
That essentially means a Yogi just does not practice physical discipline but also keenly follows the discipline in both mental and daily chores. I feel principles like honesty and forgiveness or even compassion for that matter are not skin deep, and it necessitates a complete lifestyle change and any individual wanting to embrace the yogic life also needs to look at ways to alter their way of life.
I feel one of the best ambassadors of the yogic lifestyle is Swami Vivekananda. He was calm, caring, compassionate and ever cheerful. Serious is hardly a word to describe him. Therefore the answer for whether a yogi needs to be serious is negative. The sincerity needs to be in the intent. However, I would say that they need to be 100% committed to the cause of maintaining the integrity of character and in no way can they heat on the ultimate purpose be it health reasons or otherwise. The fundamental fact is that the true essence of yoga can be realized only when the body and mind unite in purpose and salvation. Mere workout does not make a person yogi.