In Tantric philosophy, the gunas, rajas, tamas, and sattva are qualities of nature that come about as matter develops. They then go on to influence our entire lives. Each guna can be identified in us as a certain state of being. When one is rajasic, one tends to be activated, judgmental and heated. When tamasic one tends to be lethargic, depressed, and lacking in self-confidence. When sattvic one becomes balanced, understanding and compassionate.
For example, if one person criticizes another as being non-yogic, the complainer is in a rajasic state because he is being judgmental. With this imbalance, even if he is correct in his observation of the other person, he too loses his practice of yoga. If he were in a sattvic state, he would look for the goodness in the other rather than judge their negative aspects. Focusing on good qualities will enable the other to see their weaknesses, inspiring them to work on their imbalances.
On the other hand if a person is tamasic and someone compassionately points out a pattern in his behavior that is destructive, rather than seeing the observation as compassionate and helpful, he will internalize what has been said and feel victimized. If he were sattvic, however, he would be able to reflect without self-criticism and perceive ways he might change.
The process of becoming sattvic does not happen quickly, but takes effect over time with constant positive reinforcement, love and compassion. Patience and perseverance are invaluable to all aspects of your practice.