Centuries ago, Ptolemy explained the heavenly in a neat little theory. That the Earth is the centre of universe and the sun, the moon and the stars walk across the skies in predesignated paths. The universe was, of course, messier. Galileo and Copernicus discovered that universe is a mess. They came up with another neat theory - the heliocentric theory where the sun was the centre and earth and other planets revolved around it. The universe laughed and proved to be a bit more messy that these scientists thought. Today, the scientists are not sure - they have big unknowns and call them dark energy and dark mass (reminds me of Lord Voldermot).
Look at the other side of the universe - the smaller side. Scientists thought the have solved the puzzle with Quantum Mechanics. But, of course, they are still struggling with String Theory and alternatives.
Any system that has more than one parameter (player?) is by nature messy - marriage, for instance :D. Neat - but not necessarily simple - theories cannot explain complex systems completely. Beware of any neat theory that seeks to explain complex system. Actually, I am wrong. Look out for any neat theory that claims to explain complex systems. You opportunities lie exactly there. Be it science or economics or management or social sciences or market.