Why is it so?

Why is it so hard to fall in love? 
Why is it so hard to trust someone? 
Why is it so hard to let someone falls in love with you? 
Why is it so hard to let your heart smile? 
Why is it so hard for me to say 'I love you' sincerely? 
Why is it so hard for you to keep your promises?

And why is it so easy to get jealous?
Why is it so easy to cry?
Why is it so easy to let go?
Why is it so easy to lie?
Why is it so easy to break someone's heart?
Why is it so easy to make someone disappointed?