A very long time ago, I thought the popular phrase "one day at a time" was originally spoken by someone at an AA meeting. Years later I learned the actual source: the author is Christ.
He begins by talking to his disciples, instructing them how to pray sincerely and not like the hypocrites. He taught them the Lord's Prayer, and explained about forgiveness and righteousness. He spoke about where they should store up their treasures, not on earth where moth and rust destroys them, but store them in heaven; for "where your treasure is, there your heart will be also."
Then he continued by reassuring them because they were anxious about what they would have to eat and drink, and what they would have to wear, and how their needs would be met.
“Look at the birds of the air, that they do not sow, nor reap...and yet your heavenly Father feeds them. Are you not worth much more than they?”
"So do not worry about tomorrow; for tomorrow will care for itself. Each day has enough trouble of its own."
Focus on today, and just today. When tomorrow comes, that day will have its own difficulty as well.
Live each day for itself, one day at a time.