During the drug discovery and development process in the real world, expert scientists frequently encounter an unexpected obstacle that seems insurmountable. Serious issues with efficacy, toxicity, and pharmacokinetics may unexpectedly threaten the successful development of the whole project. How do experienced scientists deal with such issues? Critical thinking and problem solving are essential for success. This session features recognized experts in drug discovery and development and their fascinating and challenging stories. What went fatally wrong with a particular drug? How was the problem solved?