Complex, statistically improbable things are by their nature more difficult to explain than simple, statistically probable things.

The line states a methodological point: explanations become harder as the phenomenon to be explained becomes more complex and less likely to arise by chance. In Dawkins’s typical usage, this undercuts arguments that treat complexity as self-explanatory or as evidence for a simple, single-step cause (for example, an intelligent designer). Instead, it implies that complex order demands an account of cumulative, stepwise processes that can ratchet up improbability over time—natural selection being his paradigmatic example. The quote also distinguishes between what is common and easy to account for (simple, probable outcomes) and what requires deeper causal narratives (complex, improbable outcomes).