"Among competing hypotheses, the one with the fewest assumptions should be selected." --Occam's Razor
This is not to say the simplest answer is always the correct one, only that it is often far more likely to be correct. The only glaring exception seems to be in politics, where "if we just do one thing..." always seems to be the wrong answer (e.g., throw out immigrants, bomb Iran, whatever). Our political problems are often more complex than that. Perhaps a corollary to Occam's Razor is to distrust any answer that is simpler than the question posed.