The measure of success for System 1 is the coherence of the story it manages ~to create. The amount and quality of the data on which the story is based are largely irrelevant. When information is scarce, which is acommon occurrence, System 1 operates as a machine for jumping to conclusions.
The combination of a coherence-seeking System 1 with a lazy System 2 implies that System 2 will endorse many intuitive beliefs, which closely reflect the impressions generated by System 1.
Kahneman 2012, p.85-6