Have you had a weekend vacation destroy your carefully cultivated diet or a regular exercise regimen?
Have you noticed how if it takes 40 days to build a good habit, it takes merely 4 days to build a bad one?
Sustaining a good habit is always an uphill climb. The gradient becomes less steep with time, but it continues to remain. A bad habit, on the other hand, is a downward slope that gets steeper with each day.