Very interesting discussion... the question wouldn't even be though, how not to make mistakes.

Because we have been incarnated into this life to learn, and we learn from our mistakes. If we found a way not to make any mistakes - how would we learn?

Only one question on behalf of all mankind?

Impossible indeed since different things matter to different people.

If we ask what is the meaning of life - then we would have the answer and hence we would not be able to fulfill our mission here in this world any more, which is to learn, to teach others and to love.

If we ask what does the future hold - then we would know and make different decisions and most likely stop making an effort.

But there is one question that would be relevant to all:

how can we learn to love more?

To love others, and animals, and our environment?

Because we are in this life to love others. Love is what all living beings' existence is based on.