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$N \approx f_l \times f_i \times f_c \times L$  The first interesting term to analyse is $f_l$: $f_l$. Given the presence of the right conditions, how likely is life to emerge? Given what we know it could well be that the emergence of biological life was an incredibly fortuitous event that only happened once, here on Earth. But note that finding just a single proof for the existence (or past existence) of life on another planet (or satellite) in our solar system would change completely the picture. That would demonstrate that life can easily emerge when the conditions are approximately right, and it does not require some very special conditions. That's why it is so important to demonstrate that life is (or was) present on Mars or one of the moons of Saturn or Jupiter.