The restaurant specials are actually food they want to get rid of before they spoil
There are some restaurants that opt for the ‘food of the day’ and change their specials often, because they want to get rid of foods before they go bad. According to waiter Kathy Kniss, you should be careful when choosing soup of the day, as they generally contain fish, so the restaurant staff tries to get rid of it by turning them into specials.
The real reason behind this is that fish usually spoil faster than vegetables, for example, and they try to sell it quickly.