We don't know precisely what the ideal concoction is for life to get started, nor can we measure how close to ideal our planet is relative to others. So maybe E

We don't know precisely what the ideal concoction is for life to get started, nor can we measure how close to ideal our planet is relative to others. So maybe Earth is not the most efficient planet at developing life, and in that case, the probability equation could tip back to panspermia.