They had stumbled either upon a serious flaw in modern financial markets or into a great gambling run. Characteristically, they were not sure which it was. As Charlie pointed out, It's really hard to know when you're lucky and when you're smart.
The characters in "The Big Short" faced a dilemma regarding their situation in the financial markets. They found themselves uncertain whether they had identified a critical flaw in how these markets operated or if they were simply experiencing an extraordinary stroke of luck. This uncertainty reflects the complexities inherent in financial systems, where distinguishing between skill and chance can be quite challenging.
Charlie's observation highlights this ambiguity, emphasizing the difficulty in assessing one's success in the context of financial trading. It underlines a broader theme in the book about the unpredictable nature of markets and the thin line separating fortune from intelligence. This struggle to discern luck from wisdom is crucial as it impacts their decisions and ultimately shapes the narrative of the financial crisis.