Intelligence officers made a crucial discovery this spring after tracking Ayman al-Zawahiri, the leader of al-Qaeda, to Kabul, Afghanistan: He liked to read alone on the balcony of his safe house early in the morning.

Analysts search for that kind of pattern-of-life intelligence, any habit the CIA can exploit. In al-Zawahiri’s case, his long balcony visits gave the agency an opportunity for a clear missile shot that could avoid collateral damage.