What's the right thing?

We all have that thing that believe into
but which is right?
and which is wrong?
The right or wrong
bad or good
it all just depend on people's perspective
Is it benefit to you, then it is good
if not it is bad.

Even people, how to define bad or good then?
and of course, who been good to you then he/she is a good person
in another way, then not.
even a serial killer,
he might be bad guy to most people,
but maybe he killed a man who raped child,
and for the child's father, that serial killer is a good man to him.
But here our world likes to follow the majority
if more people believe it is right, then it is
even though it is wrong.

 So here am i, asking myself
what's left? when all things we believed in are wrong?