The Nirvana Fallacy is the name for an instance when a person does not do something because they fear that it will not turn out like they envision it in their minds.
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.
John wants to lose weight, and decides to walk 2 blocks to the subway station near his job instead of taking the bus home.
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.