There is a multitude of research into human behaviour.  Things like, what are the common reactions under certain specified conditions, what do stress factors do, testing for underlying motivation and so on.

Intuitively, recognizing much behaviour is  situational and/or affected by a variety of physical and pyschological drivers , on the whole,  an individual default behaviour is foused on their own benefit.

Altruism Aside

This is not to disregard the numerous instances of charitable behaviour or cases of putting others first.  I would argue that even in these cases, their is some element of personal satisfaction or internal desire that is driving the actions.

Healthy Cynicism

As cynical as it may seem, at the base of every interraction I have with others or other actions (both mine and others) lies a personal motivation that is “all about me”

Influencing Others

Believing this to be true is a key underpinning to understanding why others behave the way they do.  This understanding is a critical success factor supporting your influencing skills.

Money, power, friendship and respect are often used as examples of ways to drive behaviour.  (e.g., if you help me cut the grass I’ ll give you ten dollars.)

The underlying reason though will most likely be associated with psychologicla benefit ( i.e. feeling good ) or with a basic need (e.g., hunger).

Adressing both the obvious external driver together with the basic emotional needs as you try to influence others behaviours will increase your likelyhood of success.