Chastain's CIA officer says to the agency director that she's "done nothing else" over her 12 years with the agency besides work on the bin Laden case. Unlike with James Bond films, information doesn't just fall into someone's lap, or come as the result of a one-night stand with a source after a few well-shaken martinis. Chastain's character spends years vetting little bits and pieces of information as they trickle in. At one point she's devastated to learn that a lead in which she had invested enormous time and resources pursuing might ultimately be a dead end. "Confirmation bias" -- assessing a theory or a piece of information as valid because you desperately want or think it to be, and excluding other information for the same reason -- is mentioned several times throughout the film as an impediment to good intelligence work.
The film includes various shots of information mapping boards, showing the connections CIA analysts have drawn between various pieces of information and terror suspects. Intelligence work is a giant puzzle with millions of tiny pieces. Sometimes a nugget of intelligence carries no particular significance when it first pops onto an analyst's radar, but it ends up becoming valuable as more pieces are added. Vibrations in the muck can turn out to be significant in the final analysis.
This is why, for example, Russian models and businessmen in major world cities such as London, Paris and New York are encouraged to cozy up to wealthy or connected businessmen or politicians, or why Chinese students abroad are asked to feed tidbits back to the state. They are intelligence assets who are rewarded on a piecemeal, freelance basis for collecting seemingly innocuous bits and pieces about things like connections between people, contact information, business strategy, personal habits and patterns. Their job is simply to collect and feed into the system as much information as they can without assessing importance. Someone higher up the food chain takes care of assessment and puts the puzzle together. It may just be those few words that slipped from a businessman's mouth at the dinner table that, unbeknownst to him, end up being the final piece of something years in the making.
As with the shadowy world of espionage itself, the most interesting real-world lessons in "Zero Dark Thirty" are a bit farther below the surface.