No matter how closely parents try to manage their children's lives they can't possibly protect them from life's trials and tribulations. Indeed, parents shouldn't protect their children from those things. Parents should guide their children instead in how to effectively manage the challenges they'll face on their own.
Why oh why, when we leave our kid with friends, grandparents or other relatives, do they often tell us what deep down we'd rather not hear? I mean, sure on the one hand we're relieved to hear that those who were doing us the favour of watching our kids, didn't end up having to deal with a gigantic tantrum.