Python calling method without 'self'

Python calling method without 'self'

So I just started programming in python and I don't understand the whole
reasoning behind 'self'. I understand that it is used almost like a global
variable, so that data can be passed between different methods in the
class. I don't understand why you need to use it when your calling another
method in the same class. If I am already in that class, why do I have to
tell it??
example, if I have: Why do I need self.thing()?
class bla:
def hello(self):
self.thing()
def thing(self):
print "hello"