I sometimes hear my students say,"I hate myself for not being able to do this today!".
Sometimes I would jokingly congratulate them. Because they have just found things they can work on for the next few days/months/years.
Yoga is a life long practice.
Everyday is different. Your mood, body, thoughts and body feels different every day!
The practice of self-study (Svadiyaya) will make you understand how to listen to your body and control your body more over time.
That, to me is the practice of yoga. It is a practice to learn about yourself, your body and you!