As you can probably tell from this regularly occurring column, restaurants love to roll out reasonable, albeit sometimes confusing, rules for dining out. Some won’t seat you until all of your party’s present, some will limit how many times you can split your check, and some will even dictate how much you’ll tip out once that check’s been dropped.

But there’s another rule—a pair of them, actually—that restaurants frequently enforce: When a guest meets friends for happy hour, all of them are going to have to take a seat and dine in (happy hour’s not for carry-out), and all of them are likely going to order at least one drink in order to take advantage of any happy hour discounts.

Check out the Mercury's guide to 75 of the best happy hours in the city.

Happy hours, as you know, take place during any given restaurant’s slowest times: between lunch and dinner services and, at some places, right after dinner service. In other words, they go down when most of us are neither hungry nor thirsty, but not so full that we can’t pass up a good deal.

These two rules are best described as a sort of unwritten contract, which states that a customer will gladly fork over $3 or $4 for a draft beer (which they were probably going to order anyway) in order to share with their friends a $5 basket of French fries that’s been discounted to $3.

Basically the restaurant is telling guests that it’s willing to offer them fair to excellent discounts in order to fill its seats during the slowest hours of business. It’s a win-win for the restaurant and the guests. So why do these twin rules need to be enforced?

Because there are some folks who balk when told about them—and not because they’re cheap. They just might not understand that the goal is to lure people in with food specials in order to get them to take advantage of the drink specials, too. And everybody knows that the return investment on a drink—even a discounted one—is a lot better than it is with food. And if you don’t drink alcohol, you can always take advantage of food deals by ordering a soda pop. Those count as drinks, too (although it’s likely a soda will cost just as much as, if not more than, a cheap, discounted happy hour pint).

Restaurants, of course, want their guests to dine in—especially during slower times—because they’re banking on the very good chance those guests are probably going to order more than a shareable basket of fries and one adult beverage (or soda). And they’re right in thinking so, because nearly all of us will. That’s why we show up to happy hour in the first place. We can’t just expect to order take-out at happy hour prices. Dining in and ordering that drink shows that we’re committed and totally cool with upholding our end of this brief social contract in exchange for some cheap eats.

All that said, there are a couple of things to keep in mind when you’re heading out for happy hour. First, just because you can’t carry out your happy hour fare doesn’t mean you can’t carry out what you and your friends can’t eat. I write this because I’ve seen this happen. I’ve literally watched as a server told their happy hour guests that, even after they’d spent an hour eating, drinking, and chatting with their friends, that they couldn’t have their leftovers wrapped up in to-go boxes because it’s against the rules and the rules are the rules. That’s profoundly fucked up. They paid for that food, they just couldn’t finish it. There’s no reason that it should end up in the compost bin because of the “rule.” If this has ever happened to you, I’m sorry, and if it happens to you again, ask to speak with the manager, who’ll set that server straight.

Another tip? If you’re eating discounted food or drinking discounted drinks, feel free to tip on the regular amount. You don’t have to, of course, but if you’re the kind of person who’ll tip $1 instead of 60 cents on that $5 basket of fries that’s been discounted to $3, your server will see you as the kind of person who “gets” it, which virtually ensures that from now until forever you’ll be treated like gold every time you drop by.