Nairobi, July 14 -- Humans are a social sort. We thrive and have become the dominant apex species largely because of our ability to socialise, combined with our capacity for communication.

A large part of socialisation in our close-knit groups involves the ability to ask others for favours. We ask favours from friends, colleagues, family members, government officials and so on. In fact, we build up a "favour bank" with those around us.

Many people think they should merely check on someone with daily greetings-saying hi or asking how they are-so that they can then spring a surprise request on someone a few days later.

Decades-old research by Daniel Howard, a US academic and researcher, shows that this technique can increase the likeliho...