Choosing the right keywords is always challenging. There are two factors you need to consider in selecting keywords, they are relevance and popularity.
If you select a keyword or keyword phrase that is highly relevant but is never searched on, your product will never been shown to the customer. You cannot make any money from it. On the other hand, if the keyword word is incredibly popular but have nothing related to your product, you will not have a good conversion. What you only got is web traffic but they are not targeted. Generic keywords bing a lots of impression but result in few click-throughs. More than that, generic keywords do not result in qualified traffic. Unqualified traffic is less likely to convert to a sale.
You should pick a keyword that is popular enough and highly related to your product. The more relevant a term to your product, the more likely the website visitor will convert to a sale. The key to selecting good keywords is striking a balance between relevance and popularity.