Question

"The Pros and Cons of Patents" addresses several costs of obtaining a patent. According to the section "Cost 3," what problem might arise when patents are too narrow?

Answer 1

When patents are too narrow, other companies or individuals can take a patented product, tweak it slightly, and still avoid legal problems. The article uses the example of patenting the first hairbrush with bristles that lean to the side. Other companies could modify your hairbrush design without infringing on your design, at least by the legal definition of the patent.

Answer 2

According to the section "Cost 3" of "The Pros and Cons of Patents", only the creator of an idea can decide if that invention deserves the amount of time and effort  invested protecting it.  

The problems appear when patents are too narrow because this can lead to immediate confrontations between competitors or other inventors  that create a very similar product or a slight variation of a product that was patented first,  but doesn't actually violate any rights and it's appealing to the same market or targeted public.

Thus they say they came up with that idea on their own and a legal debate rises up, because there is actually no infringement but the ideas are very similar, only different in slight variations.

So those trivial circumstances can lead to a legal affair in court, because  the rules about infringement can be tangling.