Hammurabi’s code, a collection of 282 laws and standards published in 1760 BC, lists crimes and their various punishments, as well as guidelines for citizens’ conduct. Here’s some examples:
If a builder constructs a house for a man but does not make it conform to specifications so that a wall then buckles, that builder shall make that wall sound using his silver.
If a man takes in adoption a young child at birth and then rears him, that child will not be reclaimed.
If a man should blind the eye of another man, they shall blind his eye.

This is where “an eye for an eye” comes from, and the idea of reciprocity (one thing for an equal thing) is ingrained in our culture.
In business it’s the same. If you go to lunch with a coworker and pay, it’s likely that the next time they will offer to pay. In a similar vein if a sales rep takes you to lunch you often feel obligated to try their product. The feeling of reciprocating their gesture is very powerful.
In business this law is especially powerful as you work on projects together. If you go home at 5pm and the rest of the team works until midnight, you’ll feel real guilt. If this is consistent the team will feel imbalanced and you may feel the consequences in your career progression.
While this is all pretty obvious, let’s hone in on the most important law of reciprocity – it takes two people, and it has to start with one. You (yes, you!) should be the person to start the chain. Put a little extra polish on your portion of the slide deck, and your teammates will do the same. Offer to take your coworker out to lunch, and then next time they’ll offer to take you. It feels really good to be invited to lunch, and you could be the inviter first.
In our careers, we’ve seen these reciprocity-starters progress faster in their careers than the receivers. Try it today, and you may be surprised at the chain you create.