The mind alone is the cause of our happiness or misery
Most believe that it is the external conditions (persons, situations, environment, etc.) that prevent us from being happy here and now. So they strive to change the external conditions in order to feel good and happy.
However by focusing on the outside, they cannot comprehend that the obstacle is within them, that the obstacle to experiencing fullness, peace, love,and happiness but also pain and misery is their own mind, their own ego (the lower rajasotamasic ego).
On the one hand, the impure rajasotamasic mind, is anxious, distracted, extroverted, greedy, lustful, greedy, ambitious, fearful, angry, etc., it is a source of pain and misery and an impediment to experiencing the fullness of our Being (Consciousness)
On the other hand, the pure sattvic mind is dispassionate, calm, serene, luminous, harmonious, introspective and well-established source of Consciousness (which is our true nature, our spiritual Self) it is a source of harmony, joy, peace, contentment lasting happiness .
Therefore, the mind alone is the cause of our happiness or misery.