Make them into parents. The first time parent must be completely knocked sideways when they are first left alone with their little bundle of joy. Poor little thing is often a bundle of misery. He must be bewildered to find he is out of the cosy womb and left in the hands of novices. The parents meanwhile have to forgo regular sleep and keep their thoughts trained on the needs of the infant. Hobbies have to be forgotten and money spent on the child, not the latest luxury. It's great to have a child, but wow, what a steep learning curve.