Yoga philosophy has a handy way to categorise elements of the material world. In Sanskrit there are three forces called gunas: tamas, which exhibits qualities of darkness, inertia, or heaviness; rajas, which equates with raw energy, passion, dynamism; and, sattva, which is defined as Being, clarity, or spiritual essence.
Objects can be characterised according to the above scheme, and so can human moods and personalities.
Think about it. At times you’ve probably felt yourself in a heavy mood, like a dark cloud is hanging over you (tamasic). At other times, you might feel restless, with your mind jumping all over the place (rajasic). Perhaps you’ve even been blessed with grace-moments of utter calm where you feel light and clear (sattvic).
When we are perceptive enough to notice what sort of energy is influencing our behaviour, we can adjust our yoga practice accordingly.
At the times we feel lethargic and heavy, then we need to move our energy with salutes to the sun, backbends, and strong pranayamas, for instance. If our energy is wiry and unsettled, we need to put ourselves on an even keel with a soothing practice of forward bends, restorative poses and yoga nidra.
When the sun shines on our practice, on those rare days when we are under the influence of sattva, we will feel both grounded (tamas) and passionate (ragas) in equal measure.  Traditional texts suggest, then, that this is the realization of our authentic Self.

Tatah krtarthanam parinamakrama-samaptirgunanam

With that is accomplished the termination of constant transmutation of the Gunas.*
*Patanjali’s Yogasutras, translation and commentary by T.K.V. Desikachar.