In the Bhagavad Gita, Lord Krishna tells Arjuna about the three qualities — sattva, rajas and tamas. Sometimes it happens that sattva is the dominant quality in a person. In such a case, rajas and tamas are suppressed. The same can happen in the case of the other two qualities. And so, if rajas dominates, then sattva and tamas remain subdued. If tamas dominates, then sattva and rajas are subdued.
All three qualities are present in prakrti. A jivatma experiences sorrow, joy etc, because of its association with prakrti. Whether a person has sattva as the dominant quality, or one of the other two as the dominant quality depends on his karma, and also the food he consumes. We can come to a conclusion about what guna is foremost in a person by observing his behaviour, explained Valayapet Ramachariar in a discourse.
When a person’s jnanendriyas reflect pure, unconfused knowledge, then we can conclude that in the case of that person, sattva predominates. A person in whom rajas dominates, exhibits certain characteristics. He is unwilling to spend his money. He will not give even to a deserving man, even though he has the means to give. He indulges in aimless activities. He does things with a view to reaping rewards in future in this life and in the next life too. He is restless. The man with rajas also exhibits sprha — a desire for sense objects. As for the person with tamas predominating, he lacks knowledge. Excess sleep being a characteristic of a person with tamas, how can he be expected to devote time to learning? He is lazy, and lacks concentration. He cannot distinguish between good and bad, right and wrong. What a person will experience in his next birth is determined by which quality is foremost in him at the time of his death.