Reciprocity

Don't accept free drinks.

First give, then take. 

    Reciprocity is a very useful survival strategy, a form of risk management. 

Without it, humanity and countless species of animals would be long extinct. It is at the core of cooperation between people (who aren't related ) and a necessary ingredient in economic growth and wealth creation. There would be no global economy without it, there would be no economy at all. That's the good side of reciprocity. 

Reciprocity and retaliation are never apart. You start with reciprocity and end with retaliation. 

 Retaliation is the dark ugly side of reciprocity. Revenge breeds counter-revenge, and you soon find yourself in a full-scale war. 

To cut it short, I'll give you an example of how reciprocity is destroying us. 

 - 2  months ago, my neighbours invited me to dinner. They were nice but way far from entertaining. I couldn't think of a good excuse to refuse, so I went. 

As expected to be, it was tedious. Nevertheless, I felt obliged to invite them over a couple of weeks later. 

Lo and behold, a follow-up invitation from them arrived.  

  Just imagine how many dinner parties have been endured for the sake of reciprocity. 

In much the same way, if someone approaches you in the supermarket, whether to offer you a drink, a chunk of cheese, or even a handful of olives, my best advice is to refuse their offer -- unless you want to end up with a fridge full of stuff you don't even like.

That leads us to one rule: 

Never, accept a free drink

~ source : the art of thinking clearly by rolf dobelli ~