Everyone is trying to be happy because, as explained in the previous verse, sukham asyatmano rupam sarvehoparatis tanuh: when the living entity is in his original spiritual form, he is happy by nature. There is no question of miseries for the spiritual being. As Krsna is always happy, the living entities, who are His parts and parcels, are also happy by nature, but because of being put within this material world and forgetting their eternal relationship with Krsna, they have forgotten their real nature. Because every one of us is a part of Krsna, we have a very affectionate relationship with Him, but because we have forgotten our identities and are considering the body to be the self, we are afflicted by all the troubles of birth, death, old age and disease. This misconception in materialistic life continues unless and until one comes to understand his relationship with Krsna.
SB 7.13.28 Purport