The true quality and nature of yoga-abhyasa will be revealed to those who practice asana for several years, following the correct vinyasas under the immediate presence of and with direct instruction from the teacher.
On the other hand, there are people, who after doing yoga sadhana for a single day only, blame yoga for not conferring any benefits the very next day.
The real answer is known through the example of an agriculturist or farmer. Is there any agriculturist or farmer who sows seeds today and blames the science of agriculture the very next day for not producing any fruit yet?
Krishnamacharya