You know it in your own experience.

Just in proportion as you love another is it a joy and not a sorrow to give up things in order that the happiness of the other may be increased.

It is no sacrifice for a mother to give up personal enjoyment for the sake of giving it to her children.

A deeper joy is felt in the happiness of the child than could possibly have been felt in the enjoyment of the thing by herself; a sweeter, finer, profounder happiness is the enjoyment of the happiness of the beloved.

And that a little widens out the consciousness, and hence family life is one of the best schools for spiritual unfolding; for in the continual sacrifices of the family life, springing from love and rendered joyful by affection, the Self feels itself a larger Self, and reaches the sense of unity with those immediately around.