How do you know?

What is love without hate,what is hate without love,
What is pain without joy,what is joy without pain,
What is the moon without the sun, what is the sun without the moon,
How can you fall in love without heartache, how can you know heartache without falling in love,
How can you keep your feelings inside for 20 years,how can you let them out now.
How do you know you doing the right thing without doing the wrong thing,
When do you back off, when do you move forward,
When is it the right time without knowing the wrong time,
What is actions without repercussions,what is repercussions without actions,
What are lies wirhout the truth, what is the truth without lies,
What is life without death, what is death without life.
How do you know?