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There are always two opposite aspects in everything.
 
Have you watched the tree? 
It is so hard but still it allows us to make furniture out of it. 
You can sit  and put on your entire weight confidently and you are never going to get crushed. 
How come the same tree is very hard and as well soft. 
 
Have you ever watched?
Every failure has a success pattern in getting failed like
Even success has a failure pattern.
In short,
In success,
The failure pattern has to fail in the activity in order to give birth to success.
In failure,
The success pattern has to fail in the activity in order to give failure.
 
Again one more,

if you’re bad then Karma will follows you and make your life horrible…right 

But
What I heard is even people who are too good are not happy in this world. Why?

May be
What it’s trying to say is that you should practice both good and evil otherwise the unused portion of your evil will bring a kind of unhappiness in you and disturb you in day to day life.
 
Some strange things operate under the structure of society. 
To overcome you don’t need to balance your life? 
Just be aware and accept it as a part of your life.