I’ve heard this stupid advice over and over again, and what I’ve discovered in my real-life job search is that you can’t afford to waste time focusing like a laser on just one or two companies every week. Customizing your cover letter (and maybe your resume) is fine, but you can’t let that get in the way of contacting as many employers as humanly possible — by phone, mail, or whatever means necessary. You honestly don’t know where the right job will be until you make that connection, and if you waste all your time tweaking your resume for each and every potential employer, you’ll miss out.