Nearly every day, my kids come home from school and go on about some new app or game they and their mates are excited about. My younger boy invariably looks at me when he says "and it's free!" hoping that I'll smile back, but I say, "cool. I wouldn't use it". He's crestfallen . "But why!?" And... I have to pause and think and eventually I say, "well, it's kinda hard to explain".