1. The applicant did not apply for the job in the first paragraph. Instead they used tag lines and did some self promotion. Use the Knock'em Dead series to find the best introduction to your letter.These books feature letters of applicants that actually got jobs. Do your homework and find out, through networking, what the school/division is looking for.
2. The applicant made a spelling or grammatical error. A spelling or grammatical error in the first twenty words will immediately present you as someone who does not have an eye for detail. Cover letter readers begin by looking for errors. Be sure to err on the side of traditional editing, too. For example, if you use a series of three, place commas between the first, the second, and the third items. The extra comma is acceptable. Invite friends to edit your letter but be the final editor.
3. The applicant did not know how to address and sign off the business letter. I have hired many people over the years and it is a surprise that the business letter is an often overlooked format. Take time to learn the structure, learn the title of the persons in the letter and use Mr./Dr./Ms. as appropriate. Use a colon not a comma after the address (e.g., Dear Mr. Canada:). Signing off using "Sincerely yours," is appropriate. Study the shape of the business letter and do not simply duplicate a generic letter format readily available on the Internet or in books. Instead, study the business letters of those who are already in the business where you want a career. Context is everything.