Sometimes this prevents people from doing anything.
This stems from the philosophy that anything short of perfect is just as good as nothing at all.
He tells his friend, Mike...
John: I'm going to walk 2 blocks to the subway instead of taking the bus home.
Mike: HAH! Like that'll do anything! You're a freaking whale!
John: *sigh*...I guess you're right.
He then proceeds to take the bus home. That is the Nirvana Fallacy in action.