There’s no subject or way of teaching life because there’s no ‘correct’ way to live. There is a correct way to do maths, there is correct grammar and methods of science but the correct way of life is subjective and based on so many differing things such as culture, community, upbringing etc. These sub-groups form your opinions, perspective and morals and in turn these factors shape what you believe is the way to life should be lived.
Being exposed to the “complex world” where individuals face problems without the “schooling of life lesson” as you put it; experiencing that in itself is the school of life. Any failures you experience are how you learn. If you are unsure of how to face these challenges no amount of words heard or read can truly help you overcome them. The best way is to attack it head on: Fail hard and fail fast.
Trial and error. If you do not know what to do or how to do something, it is best to gather information on how NOT to do something. That is what life is and that is how you learn.
What credibility and experience do you have that adds substance to any ‘life lessons’ you aim to provide?
RE: What do we fail?