The 80/20 rule is called the "Pareto Principle." I've heard about it in business; 80% of your sales will come from 20% of your customers. I've also heard about it in relationships. And in cheating.
When looking at 80/20 from a life perspective... 20% of what happens in your life is what happens to you. 80% of that is what you do with it! This, in my opinion, is basically saying that your life is primarily under your control. I know too many people who sit around and believe the opposite. In thinking of these people they are in general the people who complain about what happens TO them. They always get the short end of the stick. Nothing goes their way. These people also seem have a hard time accepting responsibility for their actions.
In weight loss, there is also an 80/20 rule. This rule states that weight loss is a result of 80% of your diet (what you eat; not being on a diet) and 20% of your exercise.
This means that you need to know what you're eating. Whether you use a points style program or do it on your own, you must pay attention to what is going into your body. It's important to track your calories, as well as other nutrients. The top three values I pay attention to are calories, fat, and sodium. I use an online program to track these values, and more (carbohydrates, vitamins, minerals).
The type of foods you eat also play a role. Yes, a calorie is a calorie. Your body doesn't know if it's from a piece of cake or an apple. The quality of those foods does matter though. There are a lot more carbohydrates in that cake. There are a lot more nutrients in that apple. Also? You can eat a lot more healthy foods in a day than you can eat unhealthy foods. You'd be amazed at how much it feels like you're eating sometimes when you count calories and eat healthy. I've had days when I've thought "oh my gosh, I have to eat MORE?"
Hmm...On a personal note, I've not had any difficulty with that lately. Which means? I'm eating more unhealthy foods. I'm within my calorie range, but the quality could be better. I'd rather have a hard time getting there than easily getting there by enjoying a cupcake.
I think that this is when I remind you how important it is for you to research calories, calculate what you need, calculate what you burn in a day just living, calculate what you need to burn in order to lose weight. In order to lose weight, you need a calorie deficit.
Here's the easy example:
One pound is 3500 calories. Person A has decided to start losing weight. Currently she eats 2000 calories a day. This is more calories than she needs (based on her weight, height). If she takes her consumption down to 1500 calories a day, she's creating a deficit of 500 (2000-1500=500). Just taking 500 calories out of her daily diet will result in a one pound a week weight loss (500*7=3500).
Obviously as she loses weight, her needs will change. She should be careful to NEVER go below 1200 calories though, as that's unhealthy and will harm her body.
I think that sometimes people will think "oh I can eat these cookies, I'm going to workout later. I'll just burn them off." I can understand that thought process. I've been guilty of that. More than once or twice. Yes, when you workout, you burn calories. However, it's not that simple. Remember, exercise is only 20% of the weight loss game. You can't expect to get results if you're being healthy only 20% of the time. That 80% is SO important.
When I started my journey, I focused mainly on diet, then added small amounts of exercise. I saw results immediately; without the exercise part. I added it though, just small amounts...A 30 minute nightly walk on the treadmill, at a pace that now is too slow for me.
Over time your body will adjust, so you will need to continue to adjust your diet, and boost your exercise. You can't expect to see 100% by consistently only putting in 80% of the effort. The exercise portion is important. This is a rule to help someone lose weight.
Don't forget though, healthy eating and exercise will benefit your body greatly, even if weight loss is not your goal!