From Father's Desk

The Lord wants his children, those of us who have received the gift of faith, to proclaim the original optimistic view of creation, the love for the world which is at the heart of the Christian message. So there should always be enthusiasm in your professional work, and in your effort to build up the earthly city.
 
From St. Josemaria:
 
Christian optimism is not a sugary optimism; nor is it a mere human confidence that everything will turn out all right. It is an optimism that sinks its roots in an awareness of our freedom, and in the sure knowledge of the power of grace. It is an optimism which leads us to make demands on ourselves, to struggle to respond at every moment to God's calls.
The Forge, 659

The task for a Christian is to drown evil in an abundance of good. It is not a question of negative campaigns, or of being anti anything. On the contrary, we should live positively, full of optimism, with youthfulness, joy and peace. We should be understanding with everybody, with the followers of Christ and with those who abandon him, or do not know him at all. But understanding does not mean holding back, or remaining indifferent, but being active.
Furrow, 864

Our Lord, I insist, has given us the world for our inheritance. It is up to us to keep our souls and our minds wide awake. We have to be realistic, without being defeatist. Only a person with a callous conscience, made insensitive by routine or dulled by a frivolous attitude, can allow himself to think that evil — offence to God and harm, at times irreparable harm, to souls — does not exist in the world he sees. We have to be optimistic, but our optimism should come from our faith in the power of God who does not lose battles, and not from any human sense of satisfaction, from a stupid and presumptuous complacency.
Christ Is Passing By, 123, 8

Cheerfulness, and supernatural and human optimism, can go hand in hand with physical tiredness, with sorrow, with tears (because we have a heart), and with difficulties in our interior life or our apostolic work. He who is perfectus Deus, perfectus Homo — perfect God and perfect Man — and who enjoyed every happiness in Heaven, chose to experience fatigue and tiredness, tears and suffering... so that we might understand that if we are to be supernatural we must also be very human.
The Forge, 290