Guys are classical mechanical systems and Girls are quantum mechanical systems.
Guys:
1) Unless under the influence of other external pressures and stresses, a given force has only one reaction i.e. guys generally are deterministic systems.
2) Resistance and friction are forces that just try to return guys to their original state of inertia i.e rest. It has been termed as laziness by girls. Corollary: A guys state of mind at rest continues to be at rest unless and until acted upon by an external force.
3) In the presence of girls, guys can boil, melt, freeze or vaporize. In the presence of their fields of force guys can be malleable, ductile or brittle.
4) Guys show stochastic behavior, turbulence, hysteresis, lattice defects, coherence, entanglement, tunneling etc and other anomalous or non-classical phenomena only when under the influence of strong fields of force produced by girls.
5) With guys, only the statistical average of various micro-states (events, forces, thoughts or actions) show more complex dynamics but each individual micro-state can be represented as as 0-1, yes-no or true-false i.e. binary logic.
Girls:
1) Girls exhibit uncertainty. The thoughts and actions of a girl can never be simultaneously predicted i.e. measurement or prediction of one alters the other. Corollary: Girls can never do nothing i.e. due to Heisenberg's uncertainty principle, no thoughts implies infinite actions and vice versa.
2) Girls show transient growth i.e. sometimes in the presence of opposing forces, their amplitude grows with time instead of decaying. Guys view this phenomena as girls being adamant to have their way.
3) Girls exhibit quantum coherence. Each thought or action is the resultant of superposition of many causal (related through cause and effect) or non-causal (unrelated) thoughts or actions from the past, present and at times future i.e. each thought or action is the resultant of putting together many related and unrelated thoughts or actions.
4) Girls exhibit quantum entanglement. The effect of any change in the state (of a person, object, event or thought) occurring anywhere in space (and sometimes even in the future) is immediately detected and brings about a change in the girl. Commonly referred to it as a girl's intuition, girls sometimes just know certain things.
5) With girls, every micro-state (events, forces, thoughts or actions) is a probability density function i.e. nothing is binary logic. Due to uncertainty of thoughts and actions, only probability density of each micro-state can be calculated, hence no statistical averages can be computed. But, if the micro-states are allowed to evolve over time, guys can observe beautiful patterns, fractals, symmetries and ordered chaos.
FAQ:
Q: Would learning quantum mechanics help in more accurate calculation of probability densities?
A: Not Really!
In quantum mechanics either the operators (forces) that act upon a state or the effects are know, so the unknown quantity can be calculated. But with girls the operators are always unknown before they act upon anything and finding them out after they have had their effect would be too late (the quantum girl paradox)!