Psalm 90 was written by Moses. He reminds the reader about the eternal existence of God, and contrasts that with the brevity of human life. He also writes “Satisfy us in the morning with your steadfast love, that we may rejoice and be glad all our days.”
It’s an interesting idea, relating to an earlier statement that humans are “like grass that is renewed in the morning”. Only regular interaction with God can renew us, give us something to rejoice about.
The idea of God being involved in our growth and continual existence is also referred to by Paul, “I planted, Apollos watered, but God gave the growth.” A life that involves God is a satisfying one, involving regular renewal and growth. By contrast, mankind of itself is “like a flower of the field;
for the wind passes over it, and it is gone, and its place knows it no more.”