Indicate that you are not a quitter or someone who gets discouraged by rejections. You'll continue to sell your ideas as long as your bosses are open to new ideas. Try to give an example of how an idea that was initially rejected was later accepted because of your persistence and change in presentation. You might end with posing a related question to the interviewer: "How does your company encourage ideas from its employees? Does it reward those who contribute useful ideas?" These questions will give you an idea of the company's management and communication styles.