The Pareto principle (also known as the 80-20 rule, the law of the vital few, and the principle of factor sparsity) states that, for many events, roughly 80% of the effects come from 20% of the causes.
Italian economist Vilfredo Pareto, who observed in 1906 than 80% of the land in Italy was owned by 20% of the population; he developed the principle by observing that 20% of the pea pods in his garden contained 80% of the peas.
In eating healthy you can draw the same parallel, to make health a priority and eating healthy food, you do not need to be so strict that you feel bad if you have a slip. Using the 80 – 20 rule will give you enjoyment in setting your goals for healthy eating. Applying the 80 – 20, means that 80% of the time you eat healthily and do your workouts.
The 20% is your wiggle-room, which you can use to enjoy life and give yourself a treat without you feeling guilty.
You should apply the 80 – 20 rule of a period of a week, so build that in your weekly plans and enjoy life.