Why doesn't this work?

Task 2 of 3 tripped me up for quite a while, thinking there was something wrong with the logic, or for some reason the items couldn't be accessed by index number... Eventually I passed it by going the long way around:

def doubles(self):
    if self[0] == self[1]:
        return True
    else:
        return False

What I originally tried to do, which didn't work, was to return the expression directly:

        return (self[0] == self[1])

Since the expression obviously evaluates to either True or False, I have no clue why just returning it didn't work.

This also got me an earlier challenge in this course (don't remember which one now), where I had to assign an expression to a variable and then return the variable instead of returning the expression directly. So, can any Python master explain why this technique doesn't work?