This piece of advice is also common in AA circles. The implication is that even when your sobriety doesn't feel right you should not give up as the program will make sense with time. It is also used in other settings such as making a relationship work, going to church, working through depression and staying in school. It is not the same as simply being optimistic. It acknowledges the feelings of optimism may not be real but asks you to embody the intention with actions.

Exodus 20:1-2
Then God spoke all these words:
I am the Lord your God, who brought you out of the land of Egypt,
out of the house of slavery;

The Ten Commandments follow this verse. We normally think of a "command" as being a requirement that is announced, a rule, writ large. However, when God speaks, it can be heard differently. God's commands are descriptions of what is to come. As such, we can read the Ten Commandments as ten promises. God isn't saying, "here is a rule, follow it or else." God is saying, I promise you these things. Someday, you will have no interest in killing. Someday, you will love your partner so much you will have no interest in other partners. You can look forward to the day you will be so content with all that you have, you will not even think of stealing. Instead of being a source of pride for those who pretend to live them all fully, they become a source of hope for us all. And while we wait for the fulfillment of God's command promises we can all “fake it ‘till we make it!”