We don't know why this scary, bad advice persists, but once you tune it out, you'll realize that cover letters are actually very simple to write. The art of cover letter writing will really click for you once you start to hire candidates of your own, but until then, we can demystify the process.
First, remember your target audience when writing a cover letter. A hiring manager is a busy person with a full-time job, so you don’t want to waste her time. Keep your cover letter SHORT! She is also not an English teacher, college admissions representative, or AP essay grader. There’s no need to include some extravagant backstory that shows how you’ve overcome challenges or how your childhood impacted your decision to apply for this job. No one cares.
Second, think about why you’re applying for this position. Is it something you feel you’d be good at? Why? What have you done in previous positions that can prove to the hiring manager that you have the right skills? Do you enjoy the type of work that’s being produced or the tasks that will be required? All you need to do is explain why you want to work for this company and why it makes sense for the company to hire you. And if you’re having a hard time with these questions, maybe you should reconsider your application.
Ultimately, all you really need to do is think about how you would explain your reasoning behind applying for a specific job to a friend and write it down in a few short, professional sentences. You can convey your passion for the job by stating it simply and reinforce the skills listed on your resume with a few key highlights. Don’t overthink it. And certainly don't let a cover letter scare you away from a potential opportunity.