This tests your EQ (emotional intelligence, or maturity). Having stressful days, or suffering from professional disappointments, comes with the territory of any job. Everyone handles the stress of disappointment or setbacks differently. What the interviewer is gauging is how it affects or correlates with your performance level. Some people find themselves paralyzed from such 'defeat', feeling as if they failed. Others might grow defensive or angry, projecting the source of their setback onto other circumstances. Then there are those who look for any valuable lessons to be gained from such setbacks, and apply them to future situations where they'll try again with a higher likelihood of success. Discuss with the interviewer how you typically cope with delays in the workplace.