Rephrased from The Naked Scientists:
- We should investigate examples of life in the universe. But first we have to find an example.
- But ... there is a lot of life on Earth!
- Yes but we have to discount that sample due to Observer bias, so we have no examples of life in the universe.
- We should investigate examples of life in the universe. But first we have to find an example.
- But ... there is a lot of life on Earth!
- Yes but we have to discount that sample due to Observer bias, so we have no examples of life in the universe.