Each life is unique. Each living entity is different from the other. Take the physical appearances for example. There are so many outwardly parts of the body which can have different shapes and permutations and combinations are endless. And this makes each individual unique.
Nature does not seem to be using assembly line system of production but takes pains to create variations in individual parts to create a different individual every time. In fact, the natural phenomena favors distinctions. Even the products created in a assembly line begin to take different identities through their interaction with the user.
Two cars made in the identical manner give different results in the long run. It is another matter that assembly line takes away the creativity on a macro level. This is because the products will become unaffordable if we made them to order. That is why the Rolls Royce cars which are custom built are out of reach of almost all except the kings, queens and celebrities.
Life throws questions at us all the time. The questions that does not have any copy book answers. Every question is unique. It does not give us the time for preparation. We try to use whatever limited intelligence we have to scrape through the examination. We try to use the experiences of others having close match with the problems at hand. But our database is sparse and even more inefficient are the algorithms to retrieve the information.
So the life becomes a challenge. One cannot imagine what one may face at what time. Our state is like that of the sparrows which are frolicking and taking short flights out of the branches of the trees they are sitting on, only to be caught by an eagle or a kite. Hindsight is of little use in the real challenges of the life.