i don't think the expression was intended to white wash every difficult experience we have. i believe it's speaks to overcoming adversity and challenges and coming out on top, wiser and stronger. an example could be making it through college and coming out with a degree. another could be coming to terms with a traumatic experience and overcoming the feeling of being a victim. i once heard an analogy of this expression given by a well-known physician. he explained if a child was sheltered from everything, kept in an oxygen tent once the child stepped out into the world as an adult it would likely succumb to all the things in the air it never built an immunity to. he added inoculations attack a child's body with weaker strains of viruses it might be attacked by with full force in life, thus giving its immune system the opportunity to create antibodies to defeat those viruses when they do attack.