An activist friend has this phrase in his signature, so I see it every time he sends an email:

Do not be daunted by the enormity of the world's grief.
Do justly, now.
Love mercy, now.
Walk humbly, now.
You are not obligated to complete the work, but neither are you free to abandon it.
-the Talmud

It seems to sum up the enormous conundrum of being a human being…