It is no surprise to hear that we are more likely to help someone we like than someone we don't. But another factor that influences our behaviour towards others is a sense of reciprocity – the sense that you ought to do something good for someone if they have done something good for you. Psychologists have measured the effect of how much someone (Person 1) likes another person (Person 2) on the extent to which Person 1 will help Person 2 out. While there is a clear correlation here, it fades away in situations where Person 2 had previously done Person 1 a favour. In these cases, Person 1 consistently helps Person 2 out equally, regardless of how much they like them.