@tatjanastan, Yes, it's most important subject for sure and that is because, in my opinion many people most of the time find the points for the Unhappiness because many people move into the State Of Overthinking and when our mind is stressed because of Overthinking then in my opinion we will going to feel the essence of Negative thoughts and Depression. So we have to stay happy in all situations and happiness is just related to our thoughts and we have to direct our thoughts towards pleasant aspects.

Wishing you an great day and stay blessed. 🙂