Almost all the persons who do Yoga or want to do Yoga understand that Yoga is a way of life. It is a life style and not just an exercise. Even just doing Yoga exercise brings several factors into place such as eating in time, eating light, focusing the mind, etc.
Now, one who has not had this type of life style, especially the one who had radically opposite life style, prior to taking up Yoga is going to find several challenges. For example, for one to be a serious Yoga student, vegetarianism is almost a must. I am not giving the reasoning for this concept here for shortage of space and time. But, one who has eaten meat all one’s life is going to find it very hard to go vegetarian overnight. Same thing with giving up smoking or giving up alcohol.
However, one who knows the dangers of smoking to good health does not think that since smoking is hard to give up, he/she is going to continue the practice no matter what. Similarly, a serious yoga student knows what the effects of non-yogic life style is and he/she is going to attempt to achieve the Yogic life style for sure.
However, it is true that for most persons who change the life style or old habits, transitioning gradually is better and easier than going cold turkey. Those who can change immediately should not wait at all. They should jump in right away. Others should start the transition regardless of how hard it looks. A sincere and focussed practice will bring success and when continued for a sufficient time, the new methods will totally replace the old methods.
We are not graduate when we are born. We also do not graduate overnight. BUt, we do go through a long time educational process to get graduated. And once graduated, we stay that way.