You have checked your phone eleven times since breakfast, waiting for test results that were due three days ago. Logan follows intolerance of uncertainty from the Dugas model of worry — the mind treats an unanswered question as a threat, and an experiment showed that raising intolerance of uncertainty raises worry with it — through the two kinds of uncertainty, solvable and unsolvable, and the two questions that tell them apart. What was observed? People prefer a certain unpleasant outcome to an uncertain one, and worry rises and falls with intolerance of uncertainty. How was it measured? The Dugas, Freeston and Ladouceur model of worry, and the Ladouceur, Gosselin and Dugas experiment that raised and lowered intolerance of uncertainty with a gambling task. Why is it important? The feeling of not knowing shapes what we dare to wait for and how much energy waiting costs. What explanations are supported? Intolerance of uncertainty as the main driver of worry, and positive beliefs about worry keeping it going. What remains unknown? How much intolerance of uncertainty varies across cultures and across kinds of uncertainty. Sources: Dugas, Gagnon, Ladouceur and Freeston (1998), Behaviour Research and Therapy; Freeston and colleagues (1994); Ladouceur, Gosselin and Dugas (2000).