There are three types of physical exercises - for Strength, Endurance and Flexibility. Yoga provides only flexibility type of exercise. Hence, yoga alone is not enough. When yoga was evolved a few thousand years back, the lifestyle was not sedentary and perhaps in those days, yoga could be enough. Not any more.
Every individual is unique.
This fact should be remembered. Key to mental health is living a less stressful life. For all our actions, we are ourselves responsible. This fact is forgotten easily and people think that others are responsible for their problems. This fixing of blame on others is the cause of many problems.