When we do a selfless act we experience the joy from our soul – that's what we're truly are: an eternal, complete drop in the infinite ocean of pure consciousness. Our ego (which makes us feel that we're separate from others) binds us in layers and layers of conditioning, of labels and engages us in selfish acts, which only brings suffering and stress. Read about this discourse from Buddha to understand what we're missing – The Fruits of the Contemplative Life: https://www.dhammatalks.org/suttas/DN/DN02.html