Writing for readability and comprehension is more of an art than a science. A successful writer knows their audience. In grant writing, applicants have to bridge the many types of readers in their audience, from the subject matter experts to the non-specialists. Finding a happy medium with enough detail to satisfy the specialist and enough background material in the narrative to frame arguments for the generalist can be challenging. In my experience, applicants often find writing for the specialist easy, but writing for the generalist more difficult. This can often be alleviated by getting feedback from individuals who are non-specialists in your field–colleagues with different specialties or researchers in completely different areas of study.

Writing the lay summary is a different challenge altogether as it must be relevant to a non-science audience (the general public).  The summary provides an opportunity to describe the research in general terms and define why it is significant and should be funded. In many cases, the lay summary provides an opportunity to promote your research and give context to the application.

Grant writing is extremely competitive, and applications that are compelling and easy to read have a significant advantage over those that are pedantic and lackluster. 

The previous sentence provides an excellent example of word choice.  Did you have to pause to think about the definition of the descriptive words at the end of the sentence?  Think about it from your reader’s perspective-reviewers have to read (in great detail) between 6-12 applications of an average length of 30 pages (not including research contribution material).  That corresponds to roughly 300 to 600+ pages.  Would you rather be able to read and understand the information quickly or have to focus on each sentence to distill meaning?  Applications which are frustrating to read leave a poor impression on the reviewer.