Cause
and effect.  It is a concept you learn from a young age, and then you
apply it without conscious thought.  How often do you do something in
order to gain an effect of some kind?  Does this at times not become a
sort of manipulation?  An effort to control others and situations for
personal gain?  It can be quite interesting to observe the motive behind
your actions.  Are you performing a favor simply out of love and
gratitude, or to elicit a desired outcome, if only to receive more
love?  You may be surprised how much greater is that outcome when the
motivation of your actions is nothing but love.