That can be unsettling. You have an idea already why and how people would use your product. Try to let go of what you thought and see what this analysis shows you. Are there details you should change? Is your potential customer totally different? Or is what they would like to use it for different? Better to know it now so you can make a good decision about for which problem you can create a solution. If it makes you really uncertain, find a friend to share with and try to brainstorm together!
The item-by-use-analysis gave really different input than I though, what now?