There are 3 qualities that are very important in a man's life. They are:
All these 3 also corresponds to emotion, mind and action.
Say if a person only has lots and lots of intelligence and will power and not much love in him... he will become an Autocrat. He will achieve what he wants in life without any love or compassion for others. Say If he has lots and lots of Love and Intelligence, but no will power... he will be so gentle and loving to everyone, have big and amazing plans to help humanity but no will power to execute it. His plans will always stay in planning stage. And say he has lots of will power to execute anything and love but no intelligence, he becomes gullible and manipulated by others. He does everything for others and for their growth but nothing for himself, because he cant use logic and practicality to live for himself too.
So all these 3 qualities have to be in balance, in equal amount in a person's life. If you fall short in one, then its not a balanced life.
There are two kinds of happiness, temporary happiness and the long run one. If you feel happy when you eat chocolate ice cream and feel sad when you can't have any, that is temporary happiness. If you feel happy sharing knowledge and helping others and you teach because you like it, that's long term. It will stay with you even after your retired. You might continue teaching after that too. If you're not happy doing something, you cannot stay in it for long or finish what you started. Self - fulfillment is a very important factor in a person's life.
Being balanced and being fulfilled keeps a person motivated and happy in his journey through life.