Sound the fire alarm over a birthday cake candle once, and you've got a drill making people get better at evacuating.

Sound the fire alarm over a birthday cake candle several times a week, and people learn the alarm means there's no fire, no need to rush, they've got time to finish that e-mail and grab their coat.

If you never go to war with your enemy, your enemy's continued preparations are wasted money and resources (both political and economic), aren't they?