First ask him if seeking the ultimate good for oneself and others is selfish and other-ish (or altruistic). If so, then by all means let's be selfish and other-ish thuswise.

Then ask him if becoming a channel of blessing is selfish and other-ish. Let's say, each of us is like a segment of water pipe that connects with each other to provide water to many families in the neighborhood. If we deem that we are all selfish in getting all the water coming our ways every moment, then we may decide to block the flow of blessing. But that would make love impossible, for love demands giving. If one has absolutely nothing to give, then love becomes an empty word. It is in this context that we seek God's blessing so that we may become a channel of blessing to others in our midst.

Praise him for asking an insightful question. Encourage him to have his vessel of blessing filled up by God and overflowing to others.

God bless.