"My most difficult project was early in my career where I needed to make recommendations to a company based on my research. I wasn't confident in my findings or my skills because I was worried about making mistakes. I almost missed the deadline because I conducted one last focus group to confirm my findings. In the end, I was able to make recommendations that helped the business modify their product to increase sales by 20%."

Depending on your experience level, you may give an example of a school project. This example touches on a few different challenges that can occur during your market research: knowing the best tools to use and when to use them and meeting deadlines. In your example, talk about how you overcome difficulty and if possible, talk about a success with results that can be measured.