You cannot be happy thinking about yourself. The more you think about yourself and fulfilling your desires the more you become anxious and depressed especially if it is not fulfilled. All the drugs and psychotherapy is directed in trying to fulfill what you want which actually increases anxiety and distress.
The secret to happiness is trying to think about others and what they want. In that spectrum, the highest thought and consequently the highest happiness (or the most blissful experience) is to think about the instructions of a pure soul and Krishna. Fulfilling their words as opposed to yours is the secret to happiness in this world and beyond.
Try it and you will see the difference.