Ego.

It is only ego (self identity) that feels that it can make a sacrifice. The heart just is and so cannot hold a thought like this. This most beautiful part of you serves and asks for nothing in return. Because it is the purity of being it is not invested in result or recognition. It is already complete and so needs no more.
This is why nothing is more powerful or beautiful than love.
Only ego needs a thank you or acknowledgement for its kindness.
And so it is said, 'there is never any sacrifice, only the opportunity to serve.'

May all beings be happy.