Sri Chinmoy: You can maintain your joy permanently when you feel that the joy you are having is not yours. It does not come because you have done something for yourself or for God or for humanity. No! You have to feel that it is an unconditional gift from the Supreme. Then you have to feel that the joy you are experiencing is nothing other than the Supreme Himself. The Supreme has come to you in the form of Joy; so because the Supreme is permanent and eternal within you, your joy is also permanent.
First try to feel that the Supreme has given this joy to you not because of what you have done but because He loves you. It is not a result of your action but something that the Supreme Himself wants to give you. Then when you are experiencing this joy, you have to feel it is not joy as such but the Supreme Himself that you are enjoying. It is not that He has sent you joy and He is somewhere else. No, He Himself has come to you in the form of Joy. If you have this kind of inner awareness, you will be able to maintain your joy permanently, for He who has come to you as Joy is permanent and infinite. If you can see and feel Him as infinite Joy, then your joy will remain permanent.