Can someone who has always been negative and pessimistic about life change their mindset and become more positive and happy with life?

Yes, it can be done... through right understanding! rnThe Enlightened One, while providing us this understanding, says: “Failures come in almost everyone’s life. There are speed-breakers on road, aren’t they? Seeing them, one doesn’t stop there, they pass over it and move ahead.” He too has faced a lot of difficulties in his life. So how did he react to those circumstances? He reveals: “With Gnan (right knowledge), inside there remains Samadhi (bliss), and outside, there may come circumstances which are liked or not liked. Both types of circumstances come; we have to gradually keep finishing them. Whenever any clash happens or some difficulty arises, I get happy that, “Oh! my internal enemies of attachment, my false pride or greed are being axed – one of these is being cut.” Without getting hit, experience does not arise! We should be hit by adversities; and at that time if we do inner penance (of maintaining equanimity), then experience arises. Until we’ve not attained Self-Realization, there’s ignorance of the Self. Out of ignorance, this is what we have attracted all along (anger, pride, deceit, greed, attachment, hatred). And since it was filled within, with ignorance, it means we have walked away from the Soul. Therefore, we are having to take the beating. So whenever any adverse circumstance arises, we don’t have to make the other person understand, rather we must understand that I have made some mistake, if not this life, then in previous life. The other person is innocent. Whatever I am given to suffer, it is a punishment for my own past deeds. Hence, no one is at fault, it is a result of my own karmic account.” So, when we keep understanding like this, our mindset slowly slowly gets changed from negative to positive, from being pessimistic to being happy!rnHe further shares: “I too have faced a lot of beatings in life – in factory, in office, at home, in business, everywhere. Bur gradually, as I started finishing each of these turn by turn, they keep reducing and get over forever. When negativity arises, that is when Gnan (right knowledge) has to be applied. For instance, ‘Fault is of the Sufferer, Whatever Happened is Justice, Avoid Clashes, Adjust Everywhere’ This is the solution we have to bring about. rnFor this, learn to see the other person as innocent by applying the karmic principle that whatever I am suffering is a result of my own deeds and not because of the other person. And for the purpose, is the satsang. As we keep understanding what is said in the satsang, our right vision opens up.” So, first and foremost, we must attain Self-Realization. After Self-Realization, we realize how I, the pure Soul, is separate from the worldly self. Any beating in life is in the part of the worldly self and I, as a pure Soul, only know and see all that happens! And try to understand what the Enlightened One says, ‘Speed-breakers come to reduce the accidents. Whenever any difficulty, adversity or problem arises, be happy that let me bring about a solution to this which will make me progress in life!” To know more: https://www.dadabhagwan.org/path-to-happiness/self-help/positive-thinking/