One assertion made by a certain book is that there are only two root emotions: love and fear. Before I piss someone off with such a brash generalization, let me qualify that statement; the big motivating factors in peoples' lives are love and fear. Of course there's a whole gamut of other emotions that describe subtleties of feeling, but they all resolve down to some combination of the two polar opposites.
You always hear about love and hate used as opposites, but hate is really just a product of fear. Do people naturally hate one another? Not from what I've seen. A cause always exists for hatred, and I submit that there is always some kind of fear involved. People can be scared of so many things, especially in America where fear is the order of the day, and people build up thick layers of personality and rationalizations to hide the true fear lurking underneath.
Fear is the primal instinct that living creatures need to survive. It serves our physical bodies, but can have crippling effects when allowed to reverberate within the chamber of intelligent consciousness. Acting out of fear can at best give you relief, and at worst knaw away at your soul until you become an evil madman.
Love is the joyful exultation of intelligence. Animals may show varying degrees of love depending on their instincts and capacity for thought, but human love and empathy is only made possible by the acute awareness of self that humans exhibit. Acting out of love is the only possibility for true happiness. Certainly the most benevolent actions are subject to misinterpretation or perversion (especially by the highly fearful), but how much influence can one individual expect to exert in a global society of billions? Please note that I refer to a much broader emotion than romantic love; it's the feeling you get when you devote yourself to a craft, or witness the majesty of nature, or when you do something purely for someone else's benefit.
Granted, this idea is simple, and not terribly useful by itself. Life is not a simple thing; it is frought with ideological paradox, and no set of truths is absolute. Determing why we do things (even to ourselves) is often incredibly difficult, but if you allow love to be your guide and dismiss the irrational fears instilled by a paranoid society, you not only make yourself happy, but help pave the way for others to be content as well.