Sections are dense with information, but short.
The modern digital era has bread a generation of readers that expect a style of writing that conveys a whole unit of information in just a short amount of text. Whether they're reading a book, web page, news article, or a resume, most people will begin to lose interest once they reach a fifth line of text without receiving a self-contained message they could take away from. To overcome this, keep each section of your cover letter short, but substantive. Break all the complex parts into smaller, bit-sized pieces no more than five lines long.