On countless planets, conditions were perfect: the right amino acids, in the right nutrient bath and just the right amount of energy to set the whole thing off.
Then in a flash, LIFE!
These first fragile lifeforms had no other job but to grow and divide. Time and evolution would take care of the rest.
And yet, on all but a handful of these worlds, it didn't happen. All of the conditions were right, but in most cases, this early life stagnated or died out -- not because anything was wrong with its environment, but because it simply couldn't be bothered.