Long ago in an Indian kingdom, there was a poor girl who wished to marry. When her prospective in-laws came to visit her home, she greeted them graciously and bade them to sit. Her parents entertained them while, unknown to the guests, she went to the back of the house to work in the kitchen. They were planning to serve a meal with beaten rice. Ordinarily pounding the rice is the job of the servant. This family was too poor to have a servant and the girl had to pound the rice herself. She began the laborious process and quickly noticed that she was making a lot of noise. As most Indian women, she wore numerous bangles and this was causing such a racket as she flattened the rice.
On account of her poverty, she did not wear gold bangles but ones made of glass. She knew that the sound of her jingling bangles could be heard throughout the house and she did not wish her prospective in-laws to know that she was doing the work herself. She started by breaking a few bangles but found that they still made noise as she worked. Eventually she broke all her bangles save two and still they made noise by jingling against each other. Finally she broke another, leaving her with only one bangle and in silence.
This is a very old story that was told to monks, yogis and spiritual seekers of every kind. The lesson of the story is that as soon as there are two, there is discord. This means that as soon as two people practice together, there will be disagreement. Each of us has a path to walk and we must invariably walk it alone if we wish to reach the destination. Simply, we all have different minds, bodies, capacities and goals; therefore our practice must be different.
This also applies to the practice of Hatha-Yoga. Group practice is nice and offers certain advantages (group energy and motivation). However, to make real progress we must develop a personal practice. This will develop the discipline required to move forward on our path. Practicing alone also allows us to enhance our internal sensitivity and develop concentration in our practice. You can listen to your own breath and follow a sequence that is tailored to your needs, which is unavailable to you in a group setting. It makes it possible to really practice Yoga.
By practicing alone, you offer yourself the possibility to deepen and evolve your practice. This will result in real progress toward your goal. This is not to say that you should give up group classes, which can be very enjoyable. It is important for anyone wishing to genuinely practice to remember that true and transformative Yoga is purely an individual pursuit. I understand that it is not what we may want to hear but Yoga is an uphill climb that only you can do for yourself. Understand why you are practicing, where you are trying to reach, take courage and keep climbing.