To child A: Here's some money, go and buy yourself an icecream. (Goes and buys self an icecream)
Child B: She got an icecream yesterday, so I want an icecream too. (Holds out hand for the money, goes off to buy self an icecream).
Child B comes home with a box of 6 icecreams.
Parent decides that's good value, however, the intention was for the child to have ONE icecream. As a compromise, she will allow him to have 3 of the icecreams, and everyone else in the family may have one of the icecreams each.
Boy has screaming fit about them being his icecreams and his money. Boy cannot understand the concept of "Mum was only offering one icecream, regardless of the cost of the icecream and the fact that your sister spent that much and only got one for her money".
Golden family times.