You probably know the feeling or have had the experience that when a friend invites you to their party, you feel obligated to invite them to your next party as well. It's the same with a favor you owe to a colleague. In this case we talk about: Reciprocity.

Research

When a waiter at a restaurant gave a single gift to his guests, for example a mint, near the time people asked for the check. Theres was a 3% increase in tipping. If he gave two presents: Theres was a increase of 14% in tipping

BUT: If the waiter gives the second mint by saying “for you nice people”, that means by giving a compliment to the guests there was a increase of 23% in the Tip

Key takeaways

References

Cialdini, R. B., & Martin, S. (2012). Science Of Persuasion. https://www.youtube.com/watch?v=cFdCzN7RYbw&t=447s&ab_channel=influenceatwork