Don't use all-or-nothing thinking. Take each day as its own day, and don't worry about it if you mess up one day. The most important thing you can do is just get back up on the horse.
Henry Cloud (born 1956) is an American Christian self-help author. Cloud co-authored Boundaries: When to Say Yes, How to Say No to Take Control of Your Life in 1992 which sold two million copies and evolved into a five-part series.