Take a read of this awesome excerpt in relation to 80/20:
Letting Go of Perfectionism
For long-term weight loss success, aim for the 80/20 approach
Perfectionist thinking would have you believe that you are either on or off of your program. You'd view foods and behaviors as either good or bad, with good foods and behaviors causing you to lose weight and bad foods and behaviors leading to weight struggle or weight gain. Perfectionism doesn't make room for real life to occur; it doesn't allow for those everyday situations that knock you off track. These events are a normal part of life, and if your plan doesn't allow you to adapt--to exercise less when you're pressed for time, have an extra treat now and then, eat out occasionally--your forward progress and your motivation will come to a grinding halt. Try as you might, you'll never stick to any plan 100 percent of the time. And things fall apart quickly when coming up short makes you feel like a failure.
That means that the path to success is moderation in your very approach to change. You need to accept that it is okay to make healthy choices "most of the time." Success literally depends on your understanding that not only do you not have to be perfect to reach your goals, but that aiming for perfection sets you up to fail.
Defining the 80/20 Approach
One balanced approach to lifestyle change is the 80/20 model. The idea is that 80 percent of your choices are made in the planned and predictable environment of your "normal" routine and are therefore mostly healthy, while 20 percent of your decisions are made in situations that are not part of your normal routine, and therefore may include indulgences or lapses. You might be at a birthday party and have a slice of cake, or maybe you get superbusy at work and miss a few days of exercise.
At first glance, an all-or-nothing approach actually seems easier to stick to because it's so black and white; there are hard-and-fast rules that are simple to follow. The 80/20 approach, on the other hand, requires judgment and moderation; you have to make decisions and choices on the fly. For example, can you have just one of your trigger foods (one of those foods that you struggle to eat in moderation) in a given situation? Can you take a day off from exercise and get right back to the gym the next day?
The keys to making 80/20 work are that 1) understanding that the 20 percent is a normal part of life and it's better to make peace with it than attempt to avoid it altogether, and 2) you haven't "blown it" and one indulgence or lapse doesn't have to cascade into several more.