Or am I thinking of theories that are too complex? Are you thinking of X and Y as irreducible and mutually exclusive objects?
...yes? It's not a matter of complexity, though; the problem you might be alluding to is that the groups of theories we describe when we enunciate our thoughts can overlap.
Followup to: The Most Important Thing You Learned
What's the most frequently useful thing you've learned on OB - not the most memorable or most valuable, but the thing you use most often? What influences your behavior, factors in more than one decision? Please give a concrete example if you can. This isn't limited to archetypally "mundane" activities: if your daily life involves difficult research or arguing with philosophers, go ahead and describe that too.