The physical part of the triangle means your weight, organs and other things like nutrients that contribute to your health. Having a balanced physical side means eating right and exercising daily. It also means that you have the right weight for your height. Having a balaced phyical side is cruial to your well being.
The social part of the triangle is how you connect with other, family, friends, and many other things. To have the balanced social side, you need to be able to connect well with others. For example, you should be able to talk to others at school or in a work place. Keeping this side balanced will help you mantain an healthy life style.
The mental part of the triangle includes you thoughts, if you have an mental illness, how you act towards situations, attitude, feelings and more. To pursue a healthy mental side, you need to be able to control big feelings during situations. for example, you should be able to hold your urge to fight someone when in a dispute. Keeping a healthy mental state can help you in many situations beside just health.
So the idea behind the health triangle is maintain an healthy life style, now and when your older. Each side is connected to in a way they effect and help each other. If your self esteam leval is high, then mentally you love your self and socialy you can be out going because no matter what you love yourself. So no matter what the three topics will enter twin with each other no matter the situation. So this is why you need to keep them all balanced or one will over run the other or you wont be as strong in the other. That is the idea behind the Health Triangle.